A survey asked 40 people if they were concerned about the environment - 6 said that they were very concerned. Which of the following statements correctly describes how the confidence interval for the population proportion of people that are very concerned about the environment should be computed?

A. There are not 15 successes and 15 failures. A confidence interval can be computed by adding 9 successes and 9 failures.

B. There are at least 15 successes and 15 failures. A large sample confidence interval for the population proportion can be computed (phat +/- z * sqrt(p*(1-p)/n) with no additional values added.

C. There are not 15 successes and 15 failures. A confidence interval can not be done.

D. There are not 15 successes and 15 failures. A confidence interval can be computed by adding 2 successes and 2 failures.