Hello there!
Your answer would be D). Mexican-American
The reason why "Mexican-American" would be the correct answer is because this war was the war that Lee (Robert E. Lee) and Grant (Ulysses S. Grant) participated in. The reason why this war happened was because the U.S believed that Mexico was on U.S territory and killing U.S people on their own land, which they were so angered about. The U.S wanted to expand their territory for things like slavery, manifest destiny, and economical reasons.
The trick answer in this question would be answer choice "A." Answer choice "A" would be incorrect because the war was not called the "Spanish-American" war, due to the fact that this was a conflict between the U.S and Spain, it was called the "Mexican-American" war. Robert E. Lee did not participate in the Spanish-American war, which would make this answer choice wrong.
The other answer choices are wrong because Robert E. Lee and Ulysses S. Grant was not apart of those wars, which would make those answer choices incorrect.