The height h, in feet, of an object t seconds after it is dropped from a height of s feet can be modeled by the function h(t)=−16t2+s . From a branch of an oak tree 64 feet above the ground, a squirrel dropped an acorn. The acorn fell straight to the ground without hitting any branches on the way down. According to the model, approximately how long did it take the acorn to hit the ground? A: 1 second
B: 2 seconds
C: 4 seconds
D:8 seconds