What are contained in the chromosomes, and they are thought of as the units of heredity?

Genes are

At first glance, we identify two parts. Part one has the blank, a main verb and phrase. Part two the connect and and a complete sentence. It is acceptable to anticipate a main subject word or phrase. It is not letter D since it starts with because, and we already have a connector. It is not letter C since it starts with when and we already have a main connector. It is not letter A because it includes the connector which leads to an incomplete sentence. The correct answer is letter B.