Deuterium is an isotope of hydrogen. It has a mass number of two. Which describes a deuterium atom? choices:
A. a nucleus of one proton and one neutron, which is orbited by one electron
B. a nucleus of one proton, which is orbited by one neutron and one electron
C. a nucleus of one neutron, which is orbited by one electron
D. a nucleus of two neutrons which is orbited by two electrons

c

explanation:

the oldest known insects are believed to live around 400 millions ago as suggested by the fossil records.   some plants having woody stems also evolved during this time.

after the evolution of insects the first four legged species or the tetrapods evolved in shallow freshwater habitats from the intermediate species approximately 397 million years ago. the tetrapods went on conquering the land giving rise to amphibians, reptiles, mammals and birds.

the major split in tetrapods first occurred 340 million years ago branching off from amphibians.

363 million years ago when the carboniferous period began the insects started roaming on land and taking flights, following which the four limbed tetrapods adapted in the terrestrial habitat.

is it multiple choice?