Which of the following is an essential component of the "expensive tissue hypothesis" put forward by Aiello and Wheeler?

A、Humanshaveasmallerbrainsizethanexpectedfortheirbodysize
B、PrimatesshowsignificantvariationintherelationshipbetweenbodysizeandBMR
C、Humanshaveasmallergutsizethanexpectedfortheirbodysize
D、Brainistheonly"expensivetissue"inthehumanbody