问题
单项选择题
你认为下列选项中，（ ）式的开场白吸引学生注意力的效果相对较差。
A．开门见山
B．故事吸引
C．问题切入
D．幽默渲染
答案
参考答案：A
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你认为下列选项中，（ ）式的开场白吸引学生注意力的效果相对较差。
A．开门见山
B．故事吸引
C．问题切入
D．幽默渲染
参考答案：A
He is a 16-year-old boy. __1__name is Alan Brown. Alan is __2__ American high school student. He lives at __3__ Road. Art and music __4__ his favourite subjects. He loves studying and also loves sports. He usually goes swimming three or four times every week. And he walks after supper every _5__. Cool water and clean air always make him happy. American students are quite different from __6__. On Saturdays, he often has parties __7__ his friends and they always enjoy themselves. On Sundays, he usually __8__ at home and watches TV.
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，载波为
，进行抑制载波双边带调幅（DSB-SC）调制。则已调信号的带宽为（）