I'm wondering if I can use the word 'evening' in the sentence below.
-Would you like to go somewhere tomorrow night?
- I can't. I always do yoga on Thursady evening.
Students can choose between 'evening' and 'nights', and the key gives the latter as the correct anwer.
A couple of days ago I asked about time expressions in one of the threads here; I was told I could use either pattern (e.g. in the evening/in the evenings) to talk about evenings in general.
Does that mean the exercise allows two possible answers?
All four are interchangeable in your context.