When second-generation round pea plants (each of which carries both r and r genes) are crossed, find the probability that a third-generation offspring will have (a) round peas and (b) wrinkled peas?

Since both generations are both round (r) that means the thrid generation will have round peas. The probabilty for the third generation to have round peas is 100% and the probablity for the third generation to have wrinkled peas is 0%.
So your answer is A
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Ithink the answer is d.