Course Exam Question 18

Dear 365datascience,

After reviewing the explaination in question 18, I'm still having some question about this one.

Based on your explaination, the answer should not be the 2nd one because there's three 0's in the cell of the first three months of the Instagram category, the 0's are useful information but not N/A values which been regarded as missing values, right?

But the 3rd answer is still confused to me as well, since there should be all three 0's in the first 3 months, 

why the answer stated only the first 2 months without mentioning the 3rd month? It looks like an incomplete answer to me!? May need your help on this one!

Thank you!

best,

Chun