4. Раскройте скобки, используя Present Simple, Present Continuous, Present Perfect или Present Perfect Continuous.

Решение:

1. They have been living in this house since 2015. (Present Perfect Continuous, так как действие началось в прошлом и продолжается до сих пор).
2. Listen! Someone is knocking at the door. (Present Continuous, так как действие происходит в данный момент).
3. He has already finished his homework. (Present Perfect, так как действие завершено к настоящему моменту, есть указание 'already').
4. We usually go to the gym on Saturdays, but this week we are staying at home. (Present Simple для регулярного действия 'usually go' и Present Continuous для действия, происходящего на этой неделе 'are staying').
5. I have been learning Spanish for three years now. (Present Perfect Continuous, так как действие началось в прошлом и продолжается до сих пор, есть указание 'for three years now').

Ответ: have been living; is knocking; has already finished; go, are staying; have been learning.