Answer:
3^3 × 5 [Fourth option, bottom one]
Explanation:
First, 3^2 × 5^2 cannot be correct because although 3, and 5 are prime numbers 3^2 × 5^2 ≠ 135 as 3^2 × 5^2 = 225.
Second, 3 × 5 × 9 can't be right because although 3 × 5 × 9 = 135, 9 is not a prime number.
Third, 3 × 5^3 is not correct because although 3 and 5 are prime numbers, 3 × 5^3 ≠ 135 as 3 × 5^3 = 375.
The last question must be correct because it is the only remaining choice answer. Plus 3 and 5 are both prime numbers, and 3^3 × 5 = 135, 3^3 × 5 = 3 × 3 × 3 × 5 = 27 × 5 = 135.