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解释OSI模型定义的物理层？

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供电安全性是指供电系统（）供电的可靠性。

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音高的变化也就是指声音的振幅变化。

A. 正确
B. 错误

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Examine the description of the MARKS table: STD_ID NUMBER(4) STUDENT_NAME VARCHAR2(30) SUBJ1 NUMBER(3) SUBJ2 NUMBER(3) SUBJ1 and SUBJ2 indicate the marks obtained by a student in two subjects. Examine this SELECT statement based on the MARKS table: SELECT subj1+subj2 total_marks, std_id FROM marks WHERE subj1 > AVG(subj1) AND subj2 > AVG(subj2) ORDER BY total_ marks; What is the result of the SELECT statement? （）

A. The statement executes successfully and returns the student ID and sum of all marks for each student who obtained more than the average mark in each subject.
B. The statement returns an error at the SELECT clause.
C. The statement returns an error at the WHERE clause.
D. The statement returns an error at the ORDER BY clause.

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涉及产品或工艺技术的增量改进——为了迎合某个特定细分市场顾客的特定口味，而对某一产品的基础平台设计做出修改。属于企业的（）项目类型。

A. 前沿型
B. 突破型
C. 平台型
D. 衍生型

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