A:日本海沿岸
B:太平洋沿岸和濑户内海沿岸
C:内陆地区
D:东京湾地区
电阻R1、R2的电流随电压变化图象如图所示.则电阻R1的阻值为____ Ω;若把它们并联在12V的电路中,则通过R2的电流是____ A,电阻R1、R2两端的电压之比是____ .
His family are worried about him because they haven't __________ letters from him for a long time.