1.the advantage far outweigh the disadvantages.
　　2.the advantages of a are much greater than those of b.
　　3.a may be preferable to b, but a suffers from the disadvantages that...
　　4.it is reasonable to maintain that ..but it would be foolish to claim that...
　　5.for all the disadvantages, it has its compensating advantages.
　　6.like anything else, it has its faults.
　　7.a and b has several points in common.
　　8.a bears some resemblances to b.
　　9.however, the s me is not applicable to b.
　　10. a and b differ in several ways.
　　11. evidently, it has both negative and positive effects.
　　12. people used to think ..., but things are different now.
　　13. the same is true of b.
　　14. wondering　as a nbspis ,it has its drawbacks.
　　15. it is true that a ... , but the chief faults (obvious defects )are ...
　　二、原因
　　1. a number of factors are accountable for this situation.
　　a number of factors might contribute to (lead to )(account& bspfor ) the phenomenon(problem).
　　2.　the answer to this problem involves many factors.
　　3.　the phenomenon mainly stems from the fact that...
　　4. the factors that contribute to this situation include...
　　5. the change in ...largely results from the fact&n spthat...
　　6. we may　blame ...,but the real causes are...
　　7. part of the explanations for it is that ...
　　one of the most common factors (causes ) is that ...
　　another contributing factor (cause ) is ...
　　perhaps the primary actor is that …
　　but the fundamental cause is that ...
　　三、后果
　　1. it may give rise to a host of problems.
　　2. the immediate result it produces is ...
　　3. it will exercise a profound influence upon...