In an organism such as a sea urchin, administration of actinomycin D prevents RNA synthesis. ...

In an organism such as a sea urchin, administration of actinomycin D prevents RNA synthesis. However, early development up to gastrula formation can take place in the presence of actinomycin D but gastrulation cannot. This implies that __________.
 
  A) development beyond gastrulation requires actD
  B) actD is part of the normal environment of a sea urchin and serves as a developmental signal molecule
  C) actD receptors begin to form only on cell surfaces of the gastrula
  D) maternal effect genes regulate development until gastrulation
  E) immature sea urchin embryos produce actD to regulate further development