The hollow collection of undifferentiated cells that occurs after fertilization and initial mitosis is called a a. morula. b. blastocyst. c. fetus. d. placenta.

morula

Explanation:

The hollow collection of undifferentiated cells that occurs after fertilization and initial mitosis is called a morula

Morula

Explanation:

The general meaning of  blastocyst is a hollow cavity and thus it is the correct term which defines a hollow cellular mass that develops with the first week of fertilization. While morula is the stage in embryogenesis that comes before the blastocyst stage but at this stage there are 16 undifferentiated solid cells  therefore Morula is incorrect choice for this answer.

Fetus is  an advanced stage of embryo and thus it is also incorrect.  

Placenta is a tube which connect the fetus with the mother for exchange of food and nutrition. Thus it is also incorrect

the answer is lactic acid from anaerobic respiration. the acid in lactic acid is what creates sore and burning muscles. if you think about how acid burns that will give you a clue for questions like this.