Given a scientific question, generate a correct answer to it.

Ex Input:
What can be used to determine the mass of a quantity of material?

Ex Output:
molar masses

Ex Input:
What type of analysis is performed to study gene expression patterns in cells?

Ex Output:
rna analysis

Ex Input:
Why do adult herbivores in a herd surround their young?

Ex Output:
to protect them as they are vulnerable to predators