If you see double solid lines on two-lane roadways you should know that:

a) stopping is prohibited

b) backing is prohibited

c) passing is allowed

d) no passing is allowed

I believe the answer is: D. no passing is allowed

In a two lane road-ways, each line could be used for vehicles that travel on opposite directions. In such lines, passing a vehicle could be demeed as dangerous and because the risk of collision is pretty high. This become the reason why no passing allowed sign is created.