When you look at the night sky sometimes there is a full moon and sometimes the moon looks like its barely there. whydoes this happen?

because the Earths rotation and clouds are covering it

Explanation: clouds are in the way so it blocks the vision and the Earths rotation can also block out the vision of the moon

by using  production possibilities graph.  opportunity costs are key expenses in financial matters and are utilized as a part of registering money saving advantage investigation of a venture. such expenses, be that as it may, are not recorded in the record books but rather are perceived in basic leadership by processing the money costs and their subsequent benefit or misfortune.

a factory opens that mass-produces light bulbs.

explanation:

not sure if that's an answer to your questions but this is an example! : )