So difficult______ it to acquire a large vocabulary without the help of a teacher that he was close to giving up .

A．he have felt

B．have he felt

C．he did feel

D．did he feel

迫于办公场所拥挤的压力，为了减少花在交通上的时间和减少交通环境问题，一些单位采用(　)的工作模式。

A．弹性时间

B．在家工作

C．远程工作

D．虚拟办公室