需要：require, need, it is necessary for..to..,demand
　　不变：fixed, constant, stable, unchanged (unchanging)
　　担心：worry about, be concerned about, care about
　　导致，引起：cause, result in, lead to, bring about, contribute to
　　限制：limit, restrict, confine, put a limit on
　　正在做，努力：work on
　　延期相关：more time, extra time, extension, later deadline; put off, postpone, put back to, delay, (until)
　　因素：cause, factor, reason
　　合适：fit, suit, be suitable/fit/right
　　解决：solve/resolve, address, deal with, work out, tackle
　　解释：tell, explain, spell out, say how