How many cyclic structures are possible for $C_4H_6$?

In biennial plants,normally the number of carpels is:

When a wave travels in a medium,the particle displacement is given by: $y = a \sin 2\pi (bt - cx)$,where $a, b$,and $c$ are constants. The maximum particle velocity will be twice the wave velocity if

The correct order of $Cl-O$ bond order is:

Let $f(x)$ be defined for all $x > 0$ and be continuous. Let $f(x)$ satisfy $f(\frac{x}{y}) = f(x) - f(y)$ for all $x, y > 0$ and $f(e) = 1$. Then:

If $y=y(x)$ is the solution of the differential equation $\frac{5+e^x}{2+y} \cdot \frac{dy}{dx} + e^x = 0$ satisfying $y(0)=1$,then a value of $y(\log_e 13)$ is