Step 1: The modal class is the class interval having the highest frequency.
Step 2: Compare the frequencies: 5, 10, 9, 8. The maximum frequency is 10.
Step 3: The frequency 10 corresponds to the class $4000-5000$, so this is the modal class.
Step 4: The lower limit of the modal class is 4000.
Correct option is (B) 4000.