The regular teacher is ill, so a （an） ________ is teaching us to

The regular teacher is ill, so a （an） ________ is teaching us today.
A、candidate
B、applicant
C、sponsor
D、substitute
【正确答案】：D
【题目解析】：substitute 代用品；代替者。句意：正课老师病了，所以今天由代课老师教我们。