If you play with electricity，you may get an electric________.
| A．strike | B．beat | C．shock | D．knock |
Using a telescope we could see that something .
| A．is happening | B．happened | C．would happen | D．was happening |
all day, I went to bed early.
| A．Working hard | B．Worked hard | C．Having worked hard | D．To work hard |
There is a natural phenomenon scientists call the greenhouse effect.
| A．that | B．what | C．for which | D．who |
Every time I returned after an , I felt stupid because I was behind the others.
| A．ambition | B．abandon | C．absence | D．appoint |
However, the eruption itself is really exciting and I shall never forget my first sight of one.
| A．to watch | B．to be watched | C．watched | D．watching |