21. Now one of the most serious problems many people are worried about _____on the lack of adequate housing space.

A. insists        B. depends      C. agrees       D. focuses

22. _____ his wife’s strong objection, the husband insisted on putting all the money they had into the stock market, which almost drove her crazy.

A. Regardless of   B. In relation to   C. On behalf of    D. In memory of

23. The sides of the Iran nuclear negotiation reached a key point, the result of _____would have a great influence on the world peace.

    A. that       B. which       C. whom      D. them