Read this passage from the Article: The first-ever celebrity balloon was Felix the Cat, one of the leading comic strip characters back in the day. Unfortunately, the parade organizers neglected to formulate a plan for deflating Felix, so they let him fly off into the sky at the end of the day. In this passage, the word formulate means __________.
A. to make something officially become part of a law.
B. to prove that something is not true or will not work.
C. to show or reveal something to others for the first time.
D. to produce something by careful thought and effort.