When he was asked about the question where he was last night, he was _____. [ ]

A. at loss

B. in a loss

C. at a loss

D. with losses

国际上对广泛用于临床的喹诺酮类药物都限制在儿童和青少年中应用，主要原因为。

A．该类药在儿童体内生物利用度低，疗效差

B．该类药在儿童体内有可能产生有毒代谢物

C．该类药副作用较多，使用安全性差

D．该类药对幼龄动物的关节软骨有影响

E．该类药可致新生儿听力受损