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【简答题】
细菌是如何进入植物体内而引起病害?
拍照语音搜题，微信中搜索"皮皮学"使用
参考答案：
参考解析：
知识点：
皮皮学刷刷变学霸
举一反三
【单选题】Which syntax turns an existing constraint on? （）
A.
ALTER TABLE table_name ENABLE constraint_name;
B.
ALTER TABLE table_name STATUS = ENABLE CONSTRAINT constraint _ name;
C.
ALTER TABLE table_name ENABLE CONSTRAINT constraint _ name;
D.
ALTER TABLE table_name TURN ON CONSTRAINT constraint _ name;
【单选题】Which command is used to drop a constraint?
A.
ALTER TABLE MODIFY CONSTRAINT
B.
DROP CONSTRAINT
C.
ALTER CONSTRAINT DROP
D.
ALTER TABLE DROP CONSTRAINT
【单选题】Which syntax turns an existing constraint on?（）
A.
ALTER TABLE table_name ENABLE constraint_name;
B.
ALTER TABLE table_name STATUS = ENABLE CONSTRAINT constraint_name;
C.
ALTER TABLE table_name ENABLE CONSTRAINT constraint_name;
D.
ALTER TABLE table_name STATUS ENABLE CONSTRAINT constraint_name;
E.
ALTER TABLE table_name TURN ON CONSTRAINT constraint_name;
【单选题】Cooling enables the engine metals _____ their mechanical properties.
A.
to retain
B.
to remain
C.
to maintenance
D.
to have
【简答题】预算约束(budget constraint)
【简答题】借贷制约(borrowing constraint)
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