assignable variance

Im having doubts on a couple of questions:

1. An example of assignable variance in quality control:

a. equipment problem

b. Person responsible

c. Identifiable problem

d. Inadequate resource

2. changes are made to cost baseline when :

a. There is variance between what is budgeted and what is spent

b. In response to approved changes

3. CPM ( overestimates,underestimates).project duration and PERT (overestimates,underestimates) project duration.

Please help on these questions with explanations.