A mining project is composed of five activities whose three time estimates in months are given below:

Activity	Estimated duration (months)
	Optimistic time	Most likely time	Permissible time
1-2	1	1	7
1-3	2	5	8
2-4	1	1	7
3-4	2	5	14
4-5	3	6	15

The standard deviation of the project length in months is

A. 2

B. 3

C. 6

D. 9

Answer: Option B