What does circulate mean, as it is used in the paragraph?

According to stephen hawking in the "origin of the universe" lecture, "why are we here" and "where did we come from" are questions that

Insert comma today we went to the store to the post office and to the park

What is the meaning of the suffix –logy? some examples include theology, astrology, and biology. a-action or process b-science of, study of c-to make d-relating to