Unit 6 It's a mystery
1. No one knows for sure how the Moai came to be. 没人知道确切知道毛埃的来历。 for sure 是非正式的口语，意思是无疑。
2. The island also has many kinds of rock carvings written in a kind of language that exists only in this part of the world.
3. It is thought that at one time, the population of Easter Island was over 10,000.
at one time 一度，从前
4. The people never knew that cutting down the trees would cause an ecological problem. 人们当初想不到砍树会引起生态问题。
that cutting down…
5. Pretty soon the people started fighting with each other and many of them died.
The scientist knows two languages. He can speak______ English_____ French.
A. either; or B. neither; nor C. both; and D. so; that
It is______ difficult for us _____ climb up the mountain.
A. very; can’t B. too; not C. too; to D. very; to
too…for sb. to…对某人来说太??而不能
1. The river______ to the sea. It is_________ one in the country.
A. runs; the longest B. runs; a longer
C. is run; the longest D. run; a longest