Because they will grow really long if you don't
It should be an explanation on what you wanna learn about in the experiment, it should be based on prior knowledge, it is also different from a prediction
<u>A (they belong to the same group of the periodic table)</u>
<u></u>
The answer is A because C doesn't have a causal relationship, D doesn't strongly effect most chemical properties, and chemical properties remain unchanged with state of matter.