the box and monitor vs. the box and the monitor

[Sweetpumpkin]

Hello,

I have a question about 'and'. Here are two sentences:

a. The box and computer monitor are red.
b. The box and the computer monitor are red.

Which is grammatically correct? I think 'b', but I don't know how to explain why. Maybe... when we use 'A and B', the forms of A and B are same.... if A is a noun phrase, B should be the same.....? Please give me an answer.

Thank you in advance!

[Haihao]

Interesting question! I feel the difference is: a) seeing 'the box and computer monitor' as a set of two things; b) two separate things. So, grammatically both are fine. aren't they?