Penguins,seals,and tuna have body forms that permit rapid swimming,because

A)all share a common ancestor at some point in the past.
B)all of their bodies have been compressed since birth by intensive underwater pressures.
C)flying, pregnancy, and gill-breathing all require similar adaptations in form.
D)the shape is a convergent evolutionary solution to the need to reduce drag while swimming.
E)this is the only shape that will allow them to maintain a constant body temperature in water.