The correct option is D (a) and (b) above.
Be and Mg are inert to water due to the formation of an oxide film on their surface.
Calcium react with cold water to form hydroxides.
Theory
Reactivity towards water:
Be and Mg are inert to water due to the formation of an oxide film on their surface.
Magnesium decomposes hot water
Mg+2H2O⟶Mg(OH)2+H2
Mg+H2O⟶MgO+H2
Calcium, strontium and barium react with cold water to form hydroxides.