单选题 等级为A,score=100;等级为B,score=190;等级为C或D,score=60;其他,score=0.if语句,以下正确的是 ( )

A. a) if (grade = 'A' ) score = 100; else if ( grade = 'B' ) score = 90; else if ( grade = 'C' || grade = 'D' ) score = 60; else score = 0

B. b) if ( grade == 'A' ) score = 100; if ( grade == 'B' ) score = 90; if ( grade == 'C' || grade == 'D' ) score = 60; else score = 0

C. c) if ( grade == 'A' ) score = 100; else if ( grade == 'B' ) score = 90; else if ( grade == 'C' ) score = 60; else if ( grade == 'D' ) score = 60; else score = 0

D. d) if ( grade == 'A' ) score=100; else if ( grade == 'B' ) score = 90; else if ( grade == 'C' && grade == 'D' ) score = 60; else score = 0