Someone please help ASAP please

The third stage of cellular respiration is (2 points)

Pentane with molecular formula c5h12, exists in three isomeric forms. one shows linear carbon chains, another has one -ch3 groups present on the third carbon atom, and the third has two -ch3 groups present on the second carbon atom. what types of isomers are these? a. geometric isomers b. structural isomers c. halotropic isomers

Which of the following is the earliest era of earth's geologic time scale? cenozoic mesozoic precambrian paleozoic