I will look at the answers with respect to how they would affect stress: reduce or increase it.
A. Put off the project until the last minute
-This will actually increase stress! especially when the last minute comes - then the stress will be very high
B. Take a break from the project when you need it.
- I would say that this is the best answer! The emphasis here is on "when you need it" - if you need to take a break, you should and if you don't - this will potentially increase stress
C. Devote at least eight hours a day to the project.
-this does not tell us enough about the efffect on stress - the effect on stress will depend on the type of the project
D. Work on the project well into the night.
-this is a bad idea! lack of sleep can increase stress!