The center of gravity of the volume of the liquid displaced by an immersed body is called________________?

A. 5 – 10 years
B. 15 – 20 years
C. 30 – 40 years
D. 40 – 50 years

A. The particular manhole and one manhole on upstream and one manhole on downstream should remain open for 30 minutes
B. Proper tests for the presence of poisonous gases must be carried out
C. The men entering the manhole should be advised to smoke in the sewer
D. Warning signals should be erected

A. 1 in 60
B. 1 in 80
C. 1 in 10
D. 1 in 400