Word choice problem. Different opinion with my teacher
This is a sentence which I have different opinion with my teacher, of course both of us are not native speaker.
it is drawn from a jointly authored book.
One of us could have been a plumber, a pilot, or a preacher, and the praise of research skills ( ) nearly as effective as if the source were Dr. Science himself.
A. being B. was C. will be D. would have been
which choice should be filled in the ( ) ?
If someone knows this question please help me, i think it should be B. was, but apparently my teacher thinks it should be D. would have been
Thanks for your help.