The best way is a combination of several things: physical interaction with others of its own kind or specially-trained human companions, desirable features in the enclosure such as swimming pools and ledges for perching and sleeping, and toys to play with. The use of a colon in this sentence is correct because A) colons can be used in place of a period. B) colons and semi-colons are interchangeable. C) colons separate two independent clauses into sections in the sentence. D) colons should be used after independent clauses that come before lists.