Human are composed of trillions of units called cells. Within each cell is a nucleus that contains chromosomes. These chromosomes store and transmit genetic information and are made of deoxyribonucleic acid, or DNA. They come in __ matching pairs, and each member of a pair corresponds to the other in size, shape, and genetic functions..

i think the miocene epoch spans the time from 23 million to 12 million years ago.

blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium of the heart. as the ventricle contracts, blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs where it is oxygenated.

the correct answer is option d.

an appositive is a noun, noun phrase or noun clause which follows another noun or noun phrase in order to describe it or name it another way. they are usually used between commas, brackets or dashes.

the example sentence with the correct use of commas is the following:

her uncle, the man over there in the red shirt, owns the hardware store in town.