问题
单项选择题 A1型题
糖、脂肪及氨基酸三者代谢的交叉点是（）
A.丙酮酸
B.琥珀酸
C.延胡索酸
D.乙酰辅酶A
E.磷酸烯醇式丙酮酸
答案
参考答案：D
搜题请搜索小程序“爱下问搜题”
糖、脂肪及氨基酸三者代谢的交叉点是（）
A.丙酮酸
B.琥珀酸
C.延胡索酸
D.乙酰辅酶A
E.磷酸烯醇式丙酮酸
参考答案：D
以下是CLASS(课程)表和INSTRUCTOR(教师)表中所存储的数据：
| CLASS | |||
| CLASS_ID | CLASS_NAME | HOURS_CREDIT | INSTRUCTOR_ID |
| 1 | Introduction to Accounting | 3 | 4 |
| 2 | Computer Basics | 3 | 1 |
| 3 | Tax Accounting Principles | 3 | 4 |
| 4 | American History | 3 | 2 |
| 5 | Basic Engineering | 3 | |
| INSTRUCTOR | ||
| INSTRUCTOR_ID | LAST_NAME | FIRST_NAME |
| 1 | Chao | Ling |
| 2 | Vanderbilt | Herbert |
| 3 | Wigley | Martha |
| 4 | Page | Albert |
A．DELETE class_id, class_name, hours_credit, instructor_id
FROM class
WHERE instructor_id IS NULL;
B．DELETE FROM class
WHERE instructor_id NOT IN
(SELECT instructor_id
FROM class);
C．DELETE FROM
instructor NATURAL JOIN class
WHERE instructor_id IS NOT NULL;
D．DELETE FROM class
WHERE instructor_id IS NULL;