Q$3.$ What is the third variable in the population data.frame?

library$($tidyverse$)$

head$($population$)$

## # A tibble: $6$ x $3$

## country year population

##

## $1$ Afghanistan $199517586073$

## $2$ Afghanistan $199618415307$

## $3$ Afghanistan $199719021226$

## $4$ Afghanistan $199819496836$

## $5$ Afghanistan $199919987071$

## $6$ Afghanistan $200020595360$

A$.$ population

B$.$ year

C$.$ country