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

D. Be available for borrowing

Explanation. This is the best answer choice in my opinion.

free time is when all my homework and chores have been done for the day and i am "free" to do things that i enjoy doing.

usually i spend time watching television. as my favorite tv shows come on at specific times, i make sure that i finish my homework and chores well before the shows. otherwise i will have to miss them. mostly i manage to watch the shows but sometimes extra homework or chores may cause me to miss a show or two, but it is rare. anyhow if i know that i am definitely not able to catch a show in time, i will just set the video recorder to tape the show sothe evening when the weather is fine, i sometimes go for a stroll around the neighborhood with my friends. this is the time when most the neighbors have come home from work or school. we say hello to those whom we know. they are mostly friendly people and they acknowledge our greetings. once in a while we come upon unfriendly neighbors but we just ignore them and carry on. that i can watch it later.

- "the basic difference between keywords and subjects is that subjects (or "subject headings") have been predetermined, while keywords have not. a keyword is an easy place to start because you can use any word that seems to fit your search; this is called "natural language" searching."