更新表student中字段grade的值，使其在原来基础上加20分但不能超出100的限制，能够完成上述要求的SQL语句是

题目：更新表student中字段grade的值，使其在原来基础上加20分但不能超出100的限制，能够完成上述要求的SQL语句是

A. ALTER TABLE student set grade=grade+20;

B. UPDATE student set grade=grade+20 where grade<=80; UPDATE student set grade=100;

C. UPDATE student set grade=grade+20; UPDATE student set grade=100 where grade>100;

D. UPDATE student set grade=grade+20; UPDATE student set grade=100;

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