根据二次根式和分式的定义，可得x≥0且x-9≠0，
即当x≥0且x≠9时，式子有意义．
常规的舞台机械包括下列（）？
A.车台、转台、升降台、灯具
B.车台、转台、升降台、吊杆
C.车台、转台、乐池、灯具
The voters were overwhelmingly against the candidate()proposals called for higher taxes.
A. who
B. whose
C. whom
D. which
