A student observes that a popcorn kernel has a hard coat. He places the kernel in a moist paper towel and observes it for several days. He notices that the coat splits and a small root emerges. He concludes that—
water outside the seed coat exerted a pushing force, breaking the seed coat
air inside the seed coat exerted a pushing force, breaking the seed.
water outside the seed coat exerted a pulling force, breaking the seed coat.
gravity exerted a pulling force on the stem, breaking the seed coat.