Passage
the power behind a piece of popcorn is a burst of steam. each kernel of unpopped corn is a seed, within its
starchy interior is the moisture that would enable it to sprout if it were planted. heating the kernel causes
the moisture to turn to steam, exerting pressure against the starchy middle and the outer hull. when the
steam pressure reaches a critical level, the kernel blows up, turning the one-time seed inside out.

question
in order for a kernel of popcorn to burst, it is necessary for the
a)kernel to be planted in the ground
b)kernel to become saturated with water
c)starch in the center of the kernel to change to sugar
d)pressure inside the kernel to reach a certain level