See image that I have attached
Answer:
(a) cell
Explanation:
"What do scientist call the basic unit of life?
The basic unit of life is the cell. In 1838, scientists Theodor Schwann and Matthias Schleiden came up with the original version of the cell theory, which concluded that the basic unit of living things is the cell."
The three muscles that are usually used for intramuscular injection are deltoid muscle, vastus lateralis muscle and gluteus medius muscle. The one most often used for babies I think is the deltoid muscle. Please ask if you need more explaining or if you need anything else. I hope this helps. :D