How do birds hatch their eggs?

Question

$\begin{array}{1 1} \text{a)The parents of the egg will break it open} \\ \text{ b)The mother of the egg will incubate and provide warmth so that it can hatch} \\ \text{ c)Other birds will break it open} \\ \text{ d)They will put the eggs in water so that it will hatch} \end{array}$