A hydrometer

A.is used to measure the absolute pressure
B.uses the principle of buoyant force to determine specific gravities of liquids
C.is used to determine viscosities of liquids
D.is used to measure the local atmospheric pressure

Nitrogenous fertilizer is required

A.during early stages of plant growth to promote development of stems and leaves
B.to accelerate seeding or fruit formation in later stages of growth
C.for the development of the starches of potatoes and grains
D.for the development of the sugar of fruits and vegetables and the fibrous material of plants