Which process occurred frequently in the early history of the three domains on earth, and makes determining phylogenetic relationships of that time difficult?

a. horizontal gene transfer
b. alternative rna splicing
c. meiosis
d. binary fission
e. mitosis

The correct answer is - option A. horizontal gene transfer.

Explanation:

Horizontal gene transfer allows the gene movement or the flow from the genome of the one organism to another genome of the organism. It occurs in between prokaryotes of different types of species commonly even between prokaryotes and eukaryotes.  

Thus, the correct answer is - Option A. horizontal gene transfer.

when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.