有关正常心电图P波的描述错误的是（）

A.振幅在胸导联>0.2mV

B.avR导联方向向下

C.时限<0.12s

D.代表心房肌除极的电位变化

E.大部分导联上形态呈钝圆形

Theories of History
Ⅰ. How much we know about history
A. Written records exist for only a fraction of man’s time
B. The accuracy of these records is often (1) ,(1) ______
and details in them often needs improvement.
Ⅱ. Reconstruction of history before writing
A. being difficult because of the (2) of history to us (2) ______
B. the most that we can do is: use (3) (3) ______
and the knowledge of the habits of animals.
Ⅲ. Theories about history
A. Objective: to (4) the beginning and (4) ______
deduce the end of man’s story.
B. One theory believes that man continually (5) (5) ______
— (6) must be more intelligent and civilized(6) ______
than his ancestors.
—Human race will evolve into a race of (7) (7) ______
C. The second theory holds the man’s history is like a (8) (8) ______
of development.
—Modern man is not the most superior.
—Modem man may be inferior to members of (9) (9) ______
D. The third theory: Human societies repeat a cycle of stages,
but overall progress is (10) in the long historical perspective.(10) ______