The structure which prevents the entry of food into the respiratory tract is

Which of the following is associated with the conservation of forests?

Along the $X$-axis,three charges $\frac{q}{2}, -q$ and $\frac{q}{2}$ are placed at $x=0, x=a$ and $x=2a$ respectively. The resultant electric potential at $x=a+r$ (if $a \ll r$) is: ($\varepsilon_0$ is the permittivity of free space)

When an object of height $12 \ cm$ is placed at a distance from a convex lens, an image of height $18 \ cm$ is formed on a screen. Without changing the positions of the object and the screen, if the lens is moved towards the screen, another clear image is formed on the screen. The height of this image is (in $cm$)

The potential difference between $A$ and $B$ in the figure is .............. $V$.

${ }^{15}P_8 = A + 8 \cdot { }^{14}P_7 \Rightarrow A = $