Jack observes the development of frog eggs. During his observations, he noticed that within a few hours of fertilization, the single-celled zygote went through a series of cell divisions. Which of these is the best interpretation?

A. gastrulation

B. blastulation

C. cleavage

The answer is C. cleavage.

Soon after the zygote is formed, the first cleavage occurs and the 2-cell stage is formed. The second cleavage forms the 4-cell stage and the third cleavage forms the 8-cell stage, and so on. A hollow ball of thousand cells is called blastula. After blastulation, during gastrulation three distinct germ layers are formed.