a maioria dos erros são de concordância, vejam
A) How many girls are there at your party last week?
o certo: How many girls were there at your party last week?
o erro é que a frase está no passado, então o verbo to be também tem que estar.
B) Is there anybody in room 201 at the moment? (GABARITO)
C) Sarah said there is twelve people waiting.
o certo: Sarah said there were twelve people waiting.
mesmo erro da letra A, o correto é o verbo to be no passado e também plural
D) There isn’t an accident in our street last night.
o certo: There wasn't an accident in our street last night.
de novo, a mesma coisa, o certo é no passado
E) There is exercise bars so you can work out.
o certo: There are exercise bars so you can work out.
aqui é concordância entre verbo to be e plural, como temos "bars"
verbo to be tem que estar no plural