Which of the following is the right substitute for static values that can make Terraform configuration file more dynamic and reusable?

Consider the following Terraform 0.12 configuration snippet:
1. variable "vpc_cidrs" {
2. type = map
3. default = {
4. us-east-1 = "10.0.0.0/16"
5. us-east-2 = "10.1.0.0/16"
6. us-west-1 = "10.2.0.0/16"
7. us-west-2 = "10.3.0.0/16"
8. }
9. }
10.
11. resource "aws_vpc" "shared" {
12. cidr_block = _____________
13. }
How would you define the cidr_block for us-east-1 in the aws_vpc resource using a variable?

What is the default backend for Terraform?

Examine the following Terraform configuration, which uses the data source for an AWS AMI.
What value should you enter for the ami argument in the AWS instance resource?

What command does Terraform require the first time you run it within a configuration directory?