A.若R2>R0,则L1不断变暗,L2不断变亮
B.若R2>R0,则L1先变暗后变亮,L2先变亮后变暗
C.若R2<R0,则L1先变暗后变亮,L2先变亮后变暗
D.若R2<R0,则L1先变暗后变亮,L2不断变亮