题目内容

有如下关系:课程表C,主键为c-id (char (4))。
若用如下语句建立成绩表SC: CREATE TABLE SC(s-id char(6)NOT NULL,c-id char(4)NOT NULL,score Inteeer), 其中s-id为主键,c-id为外键(是C表的主键)。当执行如下语句肘,()语句不能执行。

A. INSERT SC VALUES('990101','NULL',75)
B. INSERT SC VALUES('990203','C601',80)
C. INSERT SC VALUES(NULL,'C602',93)
D. INSERT SC VALUES('990202','C604',NULL)

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