I        my homework while my parents        TV last night.[ ]

A. did, watched                

B. was doing, were watching

C. was doing, watched          

D. would do, were watching

已知电阻R₁=10Ω，R₂=40Ω．则R₁与R₂串联的总电阻为______Ω，R₁与R₂并联的总电阻为______Ω．