Whoever invented______ wheel is believed to have made______ most useful invention in______ history.
| A．a; the /; | B．the; the; / | C．the;. /; / | D．a; a; the. |
【2015·湖南】It was when we were returning home ________ I realized what a good feeling it was to have helped someone in trouble.
| A．which | B．that |
| C．where | D．how |
【2015·湖南】Only after talking to two students ________ that having strong motivation is one of the biggest factors in reaching goals.
| A．I did discover | B．did I discover |
| C．I discovered | D．discovered |
Only when Lily walked into the office ______ that she had left the contract at home.
| A． | she realized | B． | has she realized |
| C． | she has realized | D． | did she realize |
【2015•湖南】Always ________ in mind that your main task is to get this company running smoothly.
| A．to keep | B．to have kept |
| C．keep | D．have kept |
【2015·北京】_____we understand things has a lot to do with what we feel.
| A．Where | B．How | C．Why | D．When |