For this case we have that by definition, the GCF or (Greatest Common Factor) is given by the greatest common factor that divides both terms without leaving a residue.
15: 1,3,5,15
3: 1.3
Then we have the GCF of the expression is:
[tex]3t ^ 2s (t ^ 3-5s ^ 2)[/tex]
ANswer:
Option C