What is the best way to revise this sentence so that it conveys clear, concise ideas and does not change the meaning of the sentence?

i rang the doorbell, but no one came to the door, and i was sure that this was the right address, so i waited, and then i saw a curtain move.

a. i rang the doorbell, and i saw a curtain move upstairs.
b. the curtains moved in the window the moment i rang the doorbell.
c. i was sure i was at the right address, but no one came when i rang the bell.
d. i rang the doorbell, but no one came to the door. i was sure this was the right address. while i waited, i saw a curtain move.

The answer is: D. I rang the doorbell, but no one came to the door. I was sure this was the right address. While I waited, I saw a curtain move.

Explanation:

It is generally much better to have short sentences than a long involved sentence. The long sentence in the example is pretty easy to understand, but selection "D" makes the meaning clearer and easier to understand. Separate sentences cuts down on trying to figure out multiple meanings.

there is no paragraph seven here.

answer: dinner and a movie with your friends this saturday night.

opportunity cost refers to the benefits that a person or business misses out on when choosing one alternative over another. opportunity costs are easy to miss, but they can be important for decision-making. in this example, the alternative that the person will miss out on is the opportunity to have dinner and watch a movie with friends on saturday, as he will have no money left after buying the cd.