Collection of gas by the displacement of water is only possible if the gas is?

I am pretty sure it is A because you could use a test tube or beaker filled with water and turn it upside down in another container filled with water and then use a hose or something to let the gas into the test tube to displace the water. You can't have use a gas that is soluble in water. And density of the gas will determine weather it rises or sinks in water not weight.