Answer:
City A:

City B:

City B has a greater change in temperature.
Step-by-step explanation:
City A:
Let the initial temperature of city A at 8 AM = 
Temperature change from 8 AM to 9 AM: 4
rise
Temperature at 9 AM = 
Temperature change from 9 AM to 10 AM: 7
drop
Temperature at 9 AM = 
Total change in temperature =
drop
City B:
Let the initial temperature of city B at 8 AM = 
Temperature change from 8 AM to 9 AM: 6
drop
Temperature at 9 AM = 
Temperature change from 9 AM to 10 AM: 2
drop
Temperature at 9 AM = 
Total change in temperature =
drop
Therefore, the answer is:
<em>City B</em> has a greater change in temperature.