GMAT Strategy

After several months of practices, I found out that the Sentence completion section kills me. It is probably the most difficult part for Asians like me.

I have already worked out 70 questions of Official guide SC but my accuracy remains between 50% to 60%. The result is very disappointing as it seems that my SC skill is not improved. I have read the explanation 3 three times but I still cannot make it better....

Please give me some advice.