The correct answer is D. Sentence 1 is a compound sentence; Sentence 2 is a complex sentence.
Explanation:
A compound sentence is one that contains two or more ideas of the same importance linked by a semicolon or coordinating conjunctions such as and, or, but, so. On the other hand, a complex sentence contains ideas that do not have the same importance because one idea is independent or complete and the other is dependent of the independent idea, also, these are linked by subordinating conjunctions such as when, because, although, until, etc.
In the case of the sentences presented the first sentence is compound because it relates both ideas using the conjunction "and" which makes both sentences have the same importance. On the other hand, the second sentence is complex because the use of the conjunction "because" makes the sentence "Because he practices for hours a day" depend on "Michael is an expert tennis player". This means the differences between both ideas is that "Sentence 1 is a compound sentence; Sentence 2 is a complex sentence".
