Which one of the following is used in the baking of bread?

$P$ is a point on the segment joining the feet of two vertical poles of heights $a$ and $b$. The angles of elevation of the tops of the poles from $P$ are $45^{\circ}$ each. Then,the square of the distance between the tops of the poles is

The pair of gases responsible for acid rain are

If $A$ is the areal velocity of a planet of mass $M$,its angular momentum is

The symbiotic association between algae and fungi is known as -

What is a pulmonary vein?