Is the specific heat of water greater than that of sand?

Which of the substances $A, B$,or $C$ has the highest specific heat? The temperature-time graph is shown.

Which of the following is the unit of specific heat?

At which temperature is the specific heat of water minimum (in $^\circ C$)?

The $S.I.$ unit of specific heat capacity is

Water of mass $5 \ kg$ in a closed vessel is at a temperature of $20^{\circ} C$. If the temperature of the water when heated for a time of $10 \ minutes$ becomes $30^{\circ} C$, then the increase in the internal energy of the water is (Specific heat capacity of water $= 4200 \ J \ kg^{-1} \ K^{-1}$) (in $kJ$)