No one has yet succeeded in explaining the ___ of how life began.
| A．cause | B．problem | C．reason | D．puzzle |
No sooner had he arrived than he ______ to complain about the terrible weather.
| A．began | B．would begin | C．had begun | D．begins |
The measure has saved many rare animals which would ______ have died out.
| A．therefore | B．anyhow | C．furthermore | D．otherwise |
He got up late and hurried to his office, _______ the breakfast untouched.
| A．left | B．to leave | C．leaving | D．having left |
I was ______ them about my travels ______ she broke in with a story of her own.
| A．to tell; while | B．about to tell; when |
| C．was going to; while | D．telling; while |
About 270 million people in rural areas in China have no ______ to safe drinking water.
| A．entrance | B．access | C．solutions | D．sources |