Answer
A.
Work Step by Step
When G proteins are activated by receptors, they immediately bind GTP (A.). All of the other steps listed come later in the part of cell signalling involving G proteins.
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.