Answer:
D. Proteins push molecules through the cell's membrane.
Step-by-step explanation:
Active transport is a process of moving molecules from the region of lower concentration to the region of higher concentration or moving of molecules against a concentration gradient. A cell carries out active transport using energy from ATP. This type of transport is carried out using trans-membrane proteins which can cross through the membrane lipoprotein bilayer. The trans-membrane protein identifies the molecule or ion and transports them across the cell membrane. By active transport, the cells accumulate molecules such as glucose and amino acids.