Which sentence features a shift in tense?
a. she is breaking the plates she is carrying.
b. grammar has always been the secret to good writing.
c. he bought a car two weeks ago, and then he goes and buys a motorcycle last week!
d. the live broadcast will last until this evening, and then the station will return to its former programming.

Aballoon is rising vertically upwards at a velocity of 10m/s. when it is at a height of 45m from the ground, a parachute bails out from it. after 3s he opens his parachute and decelerates ata a constant rate 5m/s.when. (a) what was the height of the parachutist above the ground when he opened his parachute? (b)how far is the parachutist from the balloon at t=3s? (c)with what velocity does the parachutist hit the ground? (d)after how long does the parachutist hit the ground after his exist from the balloon?