Given the activities, time estimates and dependency relationships:

Duration $($days$)$

Activity

Predecessor

Optimistic

Most Likely

Pessimistic

A

$***$

$3$

$5$

$13$

B

$***$

$4$

$7$

$10$

C

A

$5$

$7$

$15$

D

B

$8$

$9$

$22$

What is the estimated standard deviation for the critical path?

Group of answer choices

$2\mathrm{.}78$

$2\mathrm{.}54$

$2\mathrm{.}36$

$1$