Este semestre no tengo dinero para alquilar un apartamento. (1) lo que (que/lo que) necesito es alquilar una habitación. ¿cuántos dormitorios tiene tu apartamento? —el apartamento (2) que (que/lo que) tengo tiene dos, pero el otro ya está alquilado. aunque (although) ayer conocí a un chico (3) que (que/quienes) alquila una habitación cerca de la universidad. —¿verdad? y ese chico a (4) quien (que/quien) conociste, ¿cómo se llama?

These are the correct answers:

1. lo que

2. que

3. que

4. a quien

Explanation: Just to elaborate a little on the answer, it can be added that in this exercise they are asking you to complete the sentence with the appropriate pronoun. The grammatical structure lo que can be literally translated as "that which," and que can be translated as "that." Quien and quienes can be translated as "who," in singular and plural form, respectively. So, in sentence 1, you need to use the structure lo que, since what the speaker is saying is "What I need is to rent a room." Alternatively, in sentence 2 you just need to use que, since what the speaker is saying is "The apartment that I have has two (bedrooms)."