what is the result?

Given: what is the result?

A.
ns = 50 S = 125 ns = 125 S = 125 ns = 100 S = 125

B.
ns = 50 S = 125 ns = 125 S = 125 ns = 0 S = 125

C.
ns = 50 S = 50 ns = 125 S = 125 ns = 100 S = 100

D.
ns = 50 S = 50 ns = 125 S = 125 ns = 0 S = 125