"coffee and a pizza"
Translation:кофе и пицца
«А» is never used to join nouns, only to join sentences and clauses withoin a sentence.
I think it's because that would translate to "Coffee and ONE pizza", but it asks you to translate it to "Coffee and A pizza". The verb "to be" does not exist in Russian [in present tense], so the words "is a" cannot be translated. Just typing "кофе и пицца" would be sufficient.
I'm not sure why you are explaining 'to be' here (although you're obviously 100% right, there's no 'to be' or other verb in the English version here). Since Russian doesn't have articles like 'a'/'an' and 'the' in English, один/одна/одно is commonly used instead to indicate the number one (as an amount) where in English you'd typically use 'a'/'an'. Hence, I personally think одна пицца should be accepted in this case :-)
Not really -- it simply means coffee without indicating any amount. A cup of coffe would be Чашка кофе. (However, I think the English sentence is a bit "funny" as coffee is given without any amount whereas there's 'a' pizza (i.e. the amount = "1 pizza of pizza")... For the fun of it: While we would say just "a bread" in English, you'd say "булка хлеб" in Russian to give the amount ("a bread of bread")...which probably better translates to a bread loaf / loaf of bread.