The correct answer is A. Ellos hicieron un suéter.
Explanation:
The past tense, or simple past tense, of the indicative is used in Spanish to express actions that began and ended in the past and took place in a timely manner or in a limited time space, or that interrupted another course of action also past and that It is expressed in the past imperfect.
Example:
El año pasado LLEGÓ una chica nueva a clase. Era china, de Pekín. Con un mapa nos EXPLICÓ todo sobre su país y su ciudad.
