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

If a polygon of $n$ sides has $275$ diagonals,then $n$ is equal to

Which of the following animals possesses a four-chambered heart?

Let $A = \{x_1, x_2, x_3, x_4\}$ and $B = \{y_1, y_2, y_3, y_4\}$. $A$ function $f: A \to B$ is defined. The number of one-one functions such that $f(x_i) \neq y_i$ for $i = 1, 2, 3, 4$ is equal to:

Match List-$I$ with List-$II$ and select the correct answer using the codes given below:

List-$I$	List-$II$
$(1)$ Heavy water	$(a)$ Bicarbonates of $Ca$ and $Mg$ in water
$(2)$ Temporary hard water	$(b)$ No foreign ions in water
$(3)$ Soft water	$(c)$ $D_2O$
$(4)$ Permanent hard water	$(d)$ Sulphates and chlorides of $Ca$ and $Mg$ in water

$S_1, S_2, \ldots, S_{10}$ are the speakers in a conference. If $S_1$ addresses only after $S_2$,then the number of ways the speakers address is