Help, Please AND Thanks You

Which of the following contains an error in verb voice? (10 points)

a
I would buy a large sailing yacht if I were to become rich.
b
Had I known you were going to be late, I would have started by now.
c
If I were going on this trip, I would have planned a fishing trip.
d
If I was stronger, I would be able to do more than one push up.