In the illustrated circuit, us=100cos100t V, the active power (the average power)on the load is P=UIcos φ =6W, the reactive power of the load is Q=UIsin φ =8var. We can find out that the apparent power S=sqrt(P.^2+Q.^2)=10VA, so we can get the power factor cosφ=0.8 and tan φ=3/4 .Now we want to improve the power factor to be 1, that is tan φ'=0 . The capacitor we use to parallel the load is equal to C=[P/(U.^2 )]*(tan φ-tan φ ' )= _________.Choose A,B,C or D.