In English, when you're talking about general activities you usually use plural for the object. "I eat apples every day, I read books every night" etc. That's just the grammar of English. This is not the case in Turkish. Hence the singular is correct in Turkish and the plural would be incorrect.
I learned somewhere that if you use the pronoun for third person plural in your sentence, you shouldn't use plural ending with the verb, in other words, you should use the same verb conjugation as for singular third person. Based on that, the sentence in the exercise is incorrect. Anyone else with me?