An aircraft is instructed to climb to FL330 'TO REACH FL330 BY VOR B'. If the aircraft is currently at FL250, 40 NM from VOR B, and flying at 240 knots groundspeed, what minimum rate of climb (ROC) is required?

1. 800 feet per minute
2. 1,000 feet per minute
3. 1,200 feet per minute
4. 500 feet per minute