The correct sentence is "In health class we studied these systems: endocrine, circulatory, and nervous."
You use colon to introduce a set of items. In this case, the set of items are what "we" studied in health class.
The answer is D "There are three types of flowers in this bouquet; roses, daisies, and zinnias."
The semicolon is being used perfectly and there is proper punctuation.
Locate the source of the sender and sent a letter or get into contact with whom sent this letter.