Water is important to some organism.... i think
Some objects in space are created from clouds of gas and dust. A star forms when the mass of the dust cloud is large and has enough hydrogen to start creating a protostar and sustain the nuclear fusion reaction within the core of the protostar. If the dust cloud is not dense enough, then the star formation does not take place, rather a nebula is formed, example the Horse-head nebula. So the answer is (B) A star will not form.
Uracil pairs with adenine in RNA base
Without knowing your previous answer I would say C