A newly discovered painting on wooden panel by Michelangelo must have been completed after 1507 but before 1509. It cannot have been painted earlier than 1507 because one of its central figures carries a coin that was not minted until that year. It cannot have been painted after 1509 because it contains a pigment that Michelangelo is known to have abandoned when a cheaper alternative became available in that year.

Which of the following is an assumption on which the argument depends?
- No stocks of the abandoned pigment existed after 1509.
- Michelangelo did not work on the painting over the course of several years.
- The coin depicted in the painting was known to general public in 1507.
- The wooden panel on which the painting was executed cannot be tested accurately for age.
- Michelangelo's painting style did not change between 1507 and 1509.

I find A and B to be equally strong assumptions. The explaination mentioned below wasnt convincing. Its required to make sure that Michelanglo has no stocks of the abandoned pigment after 1509. Otherwise he would have the used old stock to finish the painting in a year after 1509.

Does this mean B is the stronger choice? Did i completely miss something or is there a better way to pick the right answer?
Choice A is incorrect. We do not need to assume that no stocks of the pigment existed after 1509. The argument is concerned only with the year in which Michelangelo stopped using the pigment.

Choice B is correct. In order to conclude that the painting must have been completed before 1509 on the basis of the pigment, we must assume that he did not begin the painting before 1509 using the old pigment and complete the painting after 1509 with the new pigment.

You can apply option B to option A- Started making painting before 1507 but drew coin after 1507. This makes B a stronger choice

OOPS. Just ignore the coin part. Option B is applicable to option A

Note: option A says that no stock existed after 1509 period - anywhere, not just in Michelangelo's possession. Is it possible that the pigment still existed in the world but Michelangelo didn't use it for the stated reason? Sure - that wouldn't affect this author's claim that the painting was painted between 1507 and 1509.

For option B, however, try this: Michelangelo started painting the canvas in 1505, but put it aside for a while and then finished it in 1507, at which time he painted in the new coin. Or, Michelangelo started painting with the old pigment in 1508 and finished that particular color then. He finished the rest in 1510 but didn't need to use the particular pigment in question again - maybe it was blue and he was done with all of the blues in 1508 but added some yellow in 1510. If either of those scenarios is true, there goes the author's claim.

p.s. please remember to follow protocol. The subject of your post should be the first 5-8 words of the question itself. Thanks!