The most reliable way to make good observations is to .
A. make inferences as you observe
B. pay careful attention to what you are observing
C. draw a line through anything you need to change
D. set up a data table after you've made your observations

B--- pay careful attention to what you are observing.

Explanation:

When you go to fast when making observations, you can mess up. When you take your time and pay careful attention when making observations, there is a chance you could mess up, but it is very slim.

the answer is:

carbon dioxide