The table shows the number of planes taking off from an airport one Friday evening.
| TIME PERIOD | NO. OF PLANES |
| 3:00 – 3:30 p.m. |
 |
| 3:30 – 4:00 p.m. |
 |
| 4:00 – 4:30 p.m. |
 |
| 4:30 – 5:00 p.m. |
 |
| 5:00 – 5:30 p.m. |
 |
| 5:30 – 6:00 p.m. |
 |
| 6:00 – 6:30 p.m. |
 |
| a) | During which half-hour period did the least number of planes take off? __________ |
|
b) |
Between 4:00 and 6:00 p.m., how many planes in total took off? __________ |
|
c) |
During which 1-hour period did the greatest number of planes take off? |
|
(A) 3:00 – 4:00 (B) 3:30 – 4:30 (C) 4:00 – 5:00 (D) 4:30 – 5:30 (E) 5:00 – 6:00 |