Final answer:
Digits 1, 2, 3, and 5 appear as the unit digits of prime numbers while 4 does not, as all prime numbers other than 2 are odd, and all numbers ending with 5 and greater than 5 are multiples of 5.
Step-by-step explanation:
The student has been asked to determine which of the given digits appears as the unit digit in at least one prime number. To answer this, we assess each digit:
- A. 1: The digit 1 appears as the unit digit in some prime numbers, like 11, 31, and 41.
- B. 2: The digit 2 appears as the unit digit only in the prime number 2, as all other even numbers are not prime.
- C. 3: The digit 3 is the unit digit in several primes, such as 3, 13, and 23.
- D. 4: The digit 4 cannot be the unit digit of a prime number because numbers ending in 4 are always even and greater than 2 are not prime.
- E. 5: The digit 5 appears as the unit digit only in the prime number 5, since all other numbers ending with 5 are multiples of 5 and are not prime.
Therefore, the unit digits of prime numbers from the options given are 1, 2, 3, and 5.