4.
如图所示, \(C\)\({\,\!}_{1}=6 μF\), \(C\)\({\,\!}_{2}=3 μF\), \(R\)\({\,\!}_{1}=3 Ω\), \(R\)\({\,\!}_{2}=6 Ω\),电源电动势 \(E\)\(=18 V\),内阻不计。下列说法正确的是( )
A.开关\(S\)断开时, \(a\)、 \(b\)两点电势相等
B.开关\(S\)闭合后, \(a\)、 \(b\)两点间的电流是\(2 A\)
C.开关\(S\)断开时 \(C\)\({\,\!}_{1}\)带的电荷量比开关\(S\)闭合后 \(C\)\({\,\!}_{1}\)带的电荷量大
D.不论开关\(S\)断开还是闭合, \(C\)\({\,\!}_{1}\)带的电荷量总比 \(C\)\({\,\!}_{2}\)带的电荷量大