They're OK to me. If you use the singular, balance it-the correct form of the adjective used in each question, or something similar as correct form...adjectives doesn't work for me. Singular and plural issues can be a nightmare with a lot of disagreement.
It's often not simply a matter of counting as there are a number of factors that can affect our choices- proximity, where we make a verb agree with the noun phrase nearest it rather than .taking everything into account, so some say 'there is a car and a van parked outside' because it sounds better than 'there are a...'. As you have seen yourself, different people use different forms, so it is hard to say that only one is right. With instructions, clarity is the key so why not ask a few learners and see what they prefer?
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