The 802.11n wireless networking standard supports Multiple Input Multiple Output (MIMO) technology. MIMO technology uses multiple antennas on both the transmitting and receiving devices to improve wireless performance by increasing the amount of data that can be transmitted simultaneously. 802.11a, 802.11b, and 802.11g do not support MIMO technology. Reference: CompTIA A+ Certification Exam: Core 1 - Objective 3.3

RFID stands for Radio Frequency Identification, and it is a technology that uses electromagnetic fields to identify and track objects that have RFID tags attached to them. RFID tags are small devices that store information and can be read by RFID readers. RFID is most likely used to control door access because it allows for contactless and convenient authentication of authorized personnel. For example, an employee can use an RFID card or key fob to unlock a door by holding it near an RFID reader installed on the door. The reader will scan the tag and verify its ID number with the access control system, which will grant or deny access based on the predefined rules and permissions. RFID is a common and widely used type of door access control system, as it offers security, efficiency, and flexibility.
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Some additional references for the answer are:
IP Door Access Control - Kintronics
Door Access Control: A Complete Guide | Swiftlane
Best Door Access Control System: How It Works & Features - ButterflyMX

Near Field Communication (NFC) is used for contactless mobile payment applications. A thick or metallic phone case can block the NFC signal, preventing the payment feature from working properly.