26.______life began on the earth is one of the biggest puzzles to scientists.
It is by no means clear the president can do to end the strike.
When deeply absorbed in work, ________ he often was, he would forget all about eating or sleeping.
When you are done with the book, just give it to Lucy or Helen or __________.
Nothing is so easy as ________ parents to raise their expectations of their children too high.
Not until he retired from teaching three years ago having a holiday abroad.