Answer: Choice B) 100 pieces must be defective
Assuming the sample selected is representative of the population, we have two copies of "25" in that list (row 4; row 8) out of 40 total. So 2/40 = 1/20 = 0.05 = 5% of the items should be defective out of the entire population. Again this is assuming the sample is representative.
So we take 5% of 2000 and we end up with 0.05*2000 = 100 items we expect to be defective from a sample of 2000 items. Keep in mind that the true count will probably not be 100 items but some value close around it (eg: 98 or 101). This value is an estimate and not always perfect.
If choice B said "around 100" or "about 100" or "approximately 100" then I think it would be more technically correct. I think this is what your teacher is after.
