複選題40. Which of the following descriptions about animal development are correct? (A) Muscles and liver are both derivatives of the mesoderm (B) The initial polarity of the frog and C. elegans embryo is in part determined by the site of sperm entry (C) The order of Hox genes in a certain chromosome cluster has no correlation with the order of the body parts that they control during development (D) Morphogens are membrane-bound molecules that form concentration gradient and specify cell fates at discrete concentrations (E) Germ cells are separated from other somatic tissues early in lineage during animal development