An interstate highway loop meets the primary route at both ends. the first digit of its route number is always a. even b. odd c. 2

The answer is A. even

Quick information:

3di - three digit interstate 
2di- one-digit or two-digit interstate
Bypass routes - preceded by an even number in the first digit.

Interstate highways are  identified by one or two. Odd route numbers runs north and south while even route numbers runs east and west. Even starting digit means the 3di (3-digit) meets another interstate at both ends (loop). We call them as beltways and bypasses.