**Concept: The question tests the analytical reasoning associated with Mode as a measure of Central Tendency.**

**Solution:**

**Mode **- is the number that occurs most frequently

(__Highest frequency of occurrence in the list)__

St(1)

Let us consider that L1 and L2 **together include all the numbers L has**.

So, if L= {1, 1, 3, 17, 17, 17, 20, 21,},

L1 = {1, 1, 3, **17, 17, 17**, 20} (mode 17 here)and

L2 = {3, **17, 17, 17**, 20, 21} (mode 17 here)

Also possible that the numbers of L are not included in L1 and L2

If L = {1, 1, 3, 17, 17, 17, __17, 17__, 17, 17, 20, 21,},

L1 = {1, 1, 3, 17, 17, 17} and (mode 17 here)

L2 = {17, 17, 20, 21} (mode 17 here)

*then the underlined elements are left out.*

In both cases 17 is the most repeated number with highest frequency and there is no other possible case, thus the mode of L is 17.

**Sufficient **

St (2)

We have no information of the numbers and we have already noticed(st 1) that some 17s can be left out.

Thus not sufficient. Hence **option(A).**

** **