Which question is the best scientific question? a. why does a duck eat? b. does a duck like what it eats? c. should people eat duck? d. what does a duck eat most often?

My pick for this item is the first choice, "A. Why does a duck eat?". Scientific question is the second step in the scientific method. The question may be answered initially by the experimenter forming first a hypothesis and then conduct the experiment. 

A scientific question is the second step of the scientific method, in which an experimenter asks a question that can be answered by forming a hypothesis and conducting an experiment. A scientific question should aim for an answer that verifies, explains or theorizes information.
A. Why does a duck eat is the best scientific question.

1.989×10^30 kg is the weight of the sun.