In humans, identical twins are possible because:
a. convergent extension occurs.
b. early blastomeres can form a complete embryo if isolated.
c. cytoplasmic determinants are distributed unevenly in unfertilized eggs.
d. extraembryonic cells interact with the zygote nucleus.
e. the gray crescent divides the dorsal-ventral axis into new cells.

Ascientist is investigating the effects of salinity on fish development. he places fertilized fish eggs in an aquarium that contains low salinity and observes their development. what factor would improve experimental design the most? place the fish eggs in the open ocean because that is the natural habitat include another aquarium that has normal salinity to compare to the low salinity aquarium include an aquarium that replaces salt with sugar to confirm that the effects are specific to salt grow algae with the fish eggs in order to provide adequate nutrients to the developing embryos