The answer is a. True.
If two heterozygous (Tt) cross, there is a 25% percent chance of having a TT offspring, a 25% chance of having a tt offspring, and a 50% chance of having a Tt offspring:
Parents: Tt x Tt
Offspring: TT Tt Tt tt
So, a chance of having the tt offspring is 1 of 4, which is 1/4, which is 25%.
