Answer:
Option: C is the correct answer.
        C. Periodic with period 4 and amplitude of about 15.
Step-by-step explanation:
We are given the table of values as:
Hour             1 -- 2 -- 3 --  4 --  5 -- 6 -- 7 -- 8 -- 9 -- 10 -- 11 
Number       24-41-10-32-26-38-9-31-25-39-12
of boats 
As we could see that after every 4 value the values are approximately repeating.
Hence,the data set is approximately periodic.
Also, the amplitude is calculated as:
Average of the maximum and minimum value of each set
We divide the set into 3 sets as follows:
  Hour                       1           2           3            4
Number of boat      24        41          10           32
Here we have amplitude as:
          (41-10)/2=15.5
  Hour                       5           6           7            8
Number of boat      26        38           9           31
   Amplitude is:
           (38-9)/2=14.5
 Hour                       9           10          11            12
Number of boat      25        39          12      
             Amplitude is:
             (39-12)/2=13.5
Hence, we see that the amplitude is about 15.