[观察例句]
1．He picked a book whose cover is red.
2．This is the very novel about which we've talked so much.
3．This is Mr.John for whom I bought a book yesterday.
4．There comes a time when the old must give a way to the new...
5．After listening to the scientists who had studied the problem...
6．Not only had the countries found a path to the future that did not run over the relics of the past...
