the safety of gas, the government has checked the city’s gas supply system thoroughly.
| A．To ensure | B．Ensuring | C．Having ensured. | D．To have ensured |
Do not let any failures discourage you, for you can never tell ________ close you may be to victory.
| A．how | B．that | C．which | D．where |
Microblog is a platform ________ people can express their thoughts and communicate with each other by sending posts.
| A．which | B．where | C．what | D．when |
It was not until 1938 _________ the first colour TV programme was broadcast.
| A．which | B．that | C．when | D．on which |
Mr. John was so humorous that we had a good laugh ______ the meal.
| A．at | B．over | C．in | D．between |
I don’t think it easy, even if we work hard, ______ the South Korea and the North Korea to sit down to talk at present.
| A．persuaded | B．to persuade | C．persuade | D．persuading |