**Correct option is: C) 70**

Since, highest frequency is 17 which is of the class 30-40.

\(\therefore\) Class 30-40 is the modal class of the data

Lower limit of the modal class = 30

Upper limit of the modal class = 40

\(\therefore\) Sum = 30 + 40 = 70

Hence, the sum of lower limit and upper limit of the modal class is 70.