Make sentence: In this class, there are twice more girls than boys

[nhatanh]

This dance/ twice/ girls/ boys/there.

a. In this class , there are twice more girls than boys.
b. In this class , girls are twice more than boys.
c. In this class , there are twice as many girls as boys.
d. In this class , there are twice as much girls as boys.

I choose A, but I don't know why. Can you explain to me?

Thank you very much.

[Mister Micawber]

.
No; choose C.
.
_________________
Canadian-American native speaker
who teaches English for a living at Mister Micawber's
ESL cafe: Interview with Mister Micawber