A:①④
B:①②
C:②③
D:③④
小雷想知道小灯的亮暗程度与什么因素有关,于是找来额定电流均小于0.6A、额定电压是2.5V的灯L1和额定电压是3.8V的灯L2,先后接在电源电压恒为6V的电路中,按照如图所示的电路开始探究.
下列关于激素的叙述,正确的是( )
You had better learn to _________ different kinds of problems by yourself.