There are, of course, bad teachers as well as ______.
A.good oneB.some goodC.good onesD.those good在线课程C
解析：
句意：当然有一些坏老师也有一些好老师。one 是泛指，同名异物，根据前面bad teachers，后面应用good teachers，为了避免重复，用ones来代替teachers，所以选C。