Which valve is located between the right atrium and the right ventricle?

Which group of organisms was the first to exist on Earth among the given options?

$A$ reversible engine converts one-sixth of the heat input into work. When the temperature of the sink is reduced by $62^{\circ} C$,the efficiency of the engine is doubled. The temperatures of the source and sink are:

Which is the best method for the conservation of wild relatives of plants?

The nature of electromagnetic waves is:

From the top of a hill $h$ metres high,the angles of depression of the top and the bottom of a pillar are $\alpha$ and $\beta$ respectively. The height (in metres) of the pillar is