Explanation
Increasing density means building more units or floor area on a given site, which reduces the amount of land and resources needed per unit or occupant1. This also creates a smaller footprint and maximizes the floor area ratio (FAR), which is the ratio of the total building floor area to the site area2. Increasing density can help achieve credits in the Location and Transportation category, such as Surrounding Density and Diverse Uses3.
References:
LEED v4: Neighborhood Development Guide | U.S. Green Building Council1
Floor Area Ratio - Planning Department2
LEED v4: Building Design + Construction Guide - U.S. Green Building Council3

The location valuation factor is a concept that applies to several credits under the Materials and Resources credit category in LEED v4. It means that if the purchased products or materials are extracted, manufactured, and purchased within 100 miles (160 kilometers) of the project, LEED will award the project in the credit calculations by valuing those products at 200% of their cost1. This is to incentivize the purchase of products that reduce transportation emissions and environmental impacts associated with long-distance shipping2.
2 LEED v4: Building Design + Construction Guide, Materials and Resources, p. 487-4881 LEED 2009 vs.
LEED v4: Regional Materials - LaForce, LLC.

Explanation
A 100% vegetated roof coverage best addresses both heat island effect and rainwater runoff from the roof only. A vegetated roof, also known as a green roof, is a layer of living plants that covers the roof surface. A vegetated roof reduces the heat island effect by providing shade, evapotranspiration, and insulation, lowering the roof temperature and the surrounding air temperature. A vegetated roof also reduces rainwater runoff by retaining and absorbing precipitation, decreasing the volume and peak flow of stormwater leaving the roof.
The other options are not as effective as a 100% vegetated roof coverage in addressing both heat island effect and rainwater runoff from the roof only. A 100% high-albedo roof reflects more solar radiation than a conventional roof, reducing the heat island effect, but it does not reduce rainwater runoff. A 20% high-albedo and 80% conventional roof has a lower reflectance than a 100% high-albedo roof, resulting in a higher heat island effect, and it does not reduce rainwater runoff either. A 50% standing seam copper and 50% vegetated roof has a lower vegetated area than a 100% vegetated roof, resulting in less shade, evapotranspiration, insulation, retention, and absorption, leading to a higher heat island effect and more rainwater runoff. References: LEED Green Associate Candidate Handbook, page 27; USGBC, [Sustainable Sites], page
3.

The LEED Fellow is a distinction awarded by GBCI for LEED APs who have made significant contributions to the field of green building and sustainability at a regional, national or global level. The LEED Fellow designation recognizes exceptional contributions to green building and significant professional achievement within the rapidly growing community of LEED Professionals. References: LEED Green Associate Candidate Handbook, U.S. Green Building Council resources

Explanation
LEED certification is a process that evaluates the environmental performance and sustainability of a building project based on a set of rating systems. To earn LEED certification, a project must satisfy all the mandatory requirements, or prerequisites, of the chosen rating system, and earn a minimum number of points by meeting optional criteria, or credits. The number of points determines the level of certification: Certified (40-49 points), Silver (50-59 points), Gold (60-79 points), or Platinum (80+ points)123.
Employing a LEED AP (Accredited Professional) on the project team is not a requirement for LEED certification, but it can provide an advantage, as LEED APs have demonstrated their knowledge and expertise in green building and LEED rating systems. Having a LEED AP on the project team can also earn one point under the Integrative Process credit4.
Conducting a whole-building life-cycle assessment is not a requirement for LEED certification, but it can be an option for earning points under the Building Life-Cycle Impact Reduction credit. A life-cycle assessment is a method of evaluating the environmental impacts of a building over its entire life span, from extraction of materials to disposal or reuse3.
Earning a minimum of 50 points or meeting a prerequisite is not a sufficient condition for LEED certification, as it does not account for the other prerequisites or the level of certification. A project must meet all the prerequisites and earn at least 40 points to qualify for the lowest level of certification