电源的等效变换时IS的参考方向与US电位（ ）的方向一致。
A. 升高
B. 降低
电源的等效变换仅对 电路适用，其电源 部是不等效的
Listen to the conversation and then choose the best answers.
A. Because they can be collected and analyzed.
Because they can be sent on a different route.
C. Because they can be sent back to space.
D. Because they can potentially destroy our planet.
Listen to the conversation and then choose the best answers.
Albert Einstein.
B. Christopher Columbus.
C. Neil Armstrong.
D. Henry Ford.
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