为了使反馈式振荡电路产生的信号幅度稳定，还应当加上稳幅环节。（ ）
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In the video, the 3D pinter can produce a range of stuff, they are______
A. concrete buildings、pizza
B. skulls 、babies ( model)
C. kid art、 3D pets and cars
D. all the above
The 3D printing technology has developed to the perfect, there is no room for further advancement.
A. 对
B. 错
对携带___寄存数量较大的危险品，公安机关登记___、___。
一级易燃液体，如___、___、___焦油、石脑油。
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