Select the sentence from the article that suggests
paleontologists were able to make guesses about
the dinosaur only after a close examination.

this would be in the imperative mood. it is a category of verb forms that are used to express orders,instructions,commands or requests.

the flighty purpose never is o'ertook / unless the deed go with it"

a constant variable, normally called a controlled variable, is the term for a variable that remains constant throughout an experiment, though other variables may change. an example is the water pressure for a faucet when measuring the amount of water released when the faucet is opened to various increments.