Explanation:

- Prime numbers are numbers greater than 1 that have no divisors other than 1 and themselves.

- If A1 and A2 are two distinct prime numbers, the only common divisor they can have is 1.

- Prime numbers have no other common factors apart from 1, since they are only divisible by 1 and themselves.

- Let's examine the options:

- Option 1: 3 — This can't be the highest common factor as both numbers are distinct primes.

- Option 2: 1 — This is the correct choice because distinct prime numbers only share the common factor 1.

- Option 3: 5 — This is incorrect as it does not apply to all distinct prime numbers.

- Option 4: 2 — This is not possible since not all primes are even.