30 下圖以光學十字法表示之兩個透鏡,緊密接合後的屈光度等同於下列何者?(A)-2.00DS/+6.00DC×180(B)+4.00DS/+6.00DC×180(C)-2.00DS/+4.00DC×180(D)-4.00DS/+6.00DC×090