7794. It is very difficult to retain all that you hear in the class.

✅ The correct answer is option A.
keep : have or retain possession of.

recall : bring (a fact, event, or situation) back into one’s mind; remember.

preserve : maintain (something) in its original or existing state.

conserve : protect (something, especially something of environmental or cultural importance) from harm or destruction.

retain : continue to have (something); keep possession of.

Synonym of retain is keep