In a laboratory, smokers are asked to drive using a computerized driving simulator and cover the maximum distance possible, while avoiding rear-end collisions. some volunteers are given a real cigarette to smoke immediately before the test. others smoke a fake cigarette without nicotine. the number of collisions the two groups make is to be compared. in this study, the dependent variable is:

The number of collisions.

An object, a time period, an event, an idea or any other category a person is intended to measure is known as a variable. There are two types of variables: the independent and the dependent. An independent variable is a variable that doesn't depend on other factors and doesn't change by other variables you're trying to measure. On the other hand, a dependent variable is related to another factors and changes accordingly. In this case, the dependent variable is the number of collisions.  

the answer is:

c. economic output

if you have to make a general question and respond to your thoughts, then this isn't really a question someone can you on. read the passage, form your question, and answer using your thoughts. no one else can understand how you interpreted this text if you don't tell us.