Amass extinction is defined as
a loss of 95 percent of species
an asteroid impact
a boundary between geological periods
a loss of 50 percent of species

95% of species

Explanation:

the word mass, means very large and widespread.

thats not even an aswer choice

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.