Which one of these is a reason bones are considered to be organs?

Although it may not seem like it, bones are rigid organs. In order to be classified as an organ, in addition to performing a certain function in the body, a structure must contain more than one type of tissue. So, because bones are made of both nervous and connective tissues, they meet one of the criteria of an organ. The other answer choices about cells and framework are true, but these are not reasons why bones are considered an organ.