问题补充：
Look, a group of students are playing the violin there, their teacher as the conductor.
A. in front of them stand
B. in front of them stands
C. in front of whom standing
D. in front of whom stands
答案：
A. in front of them stand
B. in front of them stands
C. in front of whom standing
(答案→)D. in front of whom stands
解析：介词+关系代词引导的定语从句，先行词为a group of students，从句是倒装结构其主语为their teacher是单数形式谓语也要用单三形式。看一群学生在那拉小提琴，老师当指挥站在他们前面。选D
