从A、B、C、D四个选项中，选出可以填入空白处的最佳选项。
21.The proportion of the world’s population with ____ to electricity will rise over the next 20 years.
A. interest B. pleasure C. access D. difficulty
22.The shy boy felt embarrassed when it comes___ going on his first date a few weeks ago.
A. to B. about C. in D. with
23.They haven't reached a conclusion because the issue is still too politically ______ in the congress.
A. conventional B. controversial C. contradictory D. concerned
24.Don't throw away our old or broken stuff any more, ____ they may be of great value ____ you put your inspiration into them.
A. when; even if B. while; as long as C. as if ; because D. as; once
