How many even numbers of $3$ different digits can be formed from the digits $1, 2, 3, 4, 5, 6, 7, 8, 9$ (repetition is not allowed)?

Let $P = \{ (x, y) | x^2 + y^2 = 1, x, y \in R \}$. Then $P$ is

If a breeder wants to introduce a disease-resistant strain, what should be the first step?

Removal of shoot tips is a very useful technique to boost the production of tea-leaves. This is because

$A$ wall has two layers $A$ and $B$, each made of a different material. Both the layers have the same thickness. The thermal conductivity of the material of $A$ is twice that of $B$. Under thermal equilibrium, the temperature difference across the wall is $36^{\circ}C$. The temperature difference across the layer $A$ is ......... $^{\circ}C$

Which is the infectious stage of $Plasmodium$?