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问题 多选题

为提高百米赛跑运动员的成绩，教练员分析了运动员跑百米全程式的录相带，测得：运动员在前7s跑了61.6m，跑到终点共用10.8s，则（　　）

A．运动员在百米全过程的平均速度大约是9.26m/s

B．运动员在前7s的平均速度是8.8m/s

C．运动员在7s未的瞬时速度是8.8m/s

D．运动员在百米的终点冲刺速度为9.26m/s

答案

A、运动员在百米全过程的平均速度大约是

.
v
=
x
t
=
100m
10.8s
≈9.26m/s，故A正确；

B、运动员在前7s的平均速度是

.
v
=
x
t
=
61.6m
7s
≈8.8m/s，故B正确；

C、D、瞬时速度是某个时刻的速度，可以用极短时间内的平均速度代替，条件不足，无法求解7s时刻速度和通过终点的速度，故C错误，D错误；

故选AB．

单项选择题

A tree’s age can be determined by counting the annual growth rings in its trunk. Each ring represents one year, and the ring’s thickness reveals the relative amount of rainfall that year. Archaeologists successfully used annual rings to determine the relative ages of ancient tombs at Pazyryk. Each tomb was constructed from freshly cut logs, and the tombs’ builders were constrained by tradition to use only logs from trees growing in the sacred Pazyryk Valley.
Which one of the following, if true, contributes most to an explanation of the archaeologists’ success in using annual rings to establish the relative ages of the tombs at the Pazyryk site ？（）

A．The Pazyryk tombs were all robbed during ancient times, but breakage of the tombs’ seals allowed the seepage of water, which soon froze permanently, thereby preserving the tombs’ remaining artifacts.

B．The Pazyryk Valley, surrounded by extremely high mountains, has a distinctive yearly pattern of rainfall, and so trees growing in the Pazyryk Valley have annual rings that are quite distinct from trees growing in nearby valleys.

C．Each log in the Pazyryk tombs has among its rings a distinctive sequence of twelve annual rings representing six drought years followed by three rainy years and three more drought years.

D．The archaeologists determined that the youngest tree used in any of the tombs was 90 years old and that the oldest tree was 450 years old.

E．All of the Pazyryk tombs contained cultural artifacts that can be dated to roughly 2300 years ago.
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单项选择题

哪一项不是髓母细胞瘤的CT表现（）

A.梗阻性脑积水

B.肿瘤明显强化

C.瘤周水肿

D.脂肪密度

E.主要发生于小脑蚓部
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