What is carried by the waves? Mass,velocity,or energy?

The figure shows a snapshot of a travelling sine wave along a string. Four elemental portions $a, b, c,$ and $d$ are indicated on the string. Which elemental portion$(s)$ has/have the maximum potential energy?

The dependence of disturbances due to two waves on time is shown in the figure. The ratio of their intensities $I_1 / I_2$ will be

$A$ travelling wave is partly reflected and partly transmitted from a rigid boundary. Let $a_i, a_r$ and $a_t$ be the amplitudes of the incident wave,reflected wave,and transmitted wave,and $I_i, I_r$ and $I_t$ be the corresponding intensities. Choose the correct alternative.

$A$ surface of area $S$ is placed perpendicular to the direction of travel of a plane wave. The energy per unit time intercepted by the surface is $E$ when the amplitude of the wave is $A$. The area of the surface is reduced to $\frac{1}{2} S$ and the amplitude of the wave is increased to $2A$. What is the energy per unit time intercepted by this smaller surface?

If the separation between the screen and the source is increased by $2\%$,what would be the effect on the intensity?