The line that draws power supply to your house from the street has 

(a) zero average current
(b) 220 V average voltage
(c) voltage and current out of phase by $90°$
(d) voltage and current possibly differing in phase $\mathrm{\varphi } \mathrm{such} \mathrm{that} \left|\mathrm{\varphi }\right|<\frac{\mathrm{\pi }}{2}$

1. (b, c)

2. (a, d)

3. (b, d)

4. (a, c)