영어 문장 두 개 중 틀린 부분을 찾아주세요

아래 두 문장 중 틀린 문장이 무엇인지, 고치는 방법도 알려주세요.
There has been a large number of rice dishes, and many of them are very simple to prepare.
Saffron was added to risotto by one of the workers, and it has been popular since then.