Load the built-in dataset co2 using:

library(dslabs)
data(co2)

Do this in RStudio so you can look at the contents of the co2 dataframe

Which of the following is true:

1. co2 is tidy data: it has one year for each row.
2. co2 is not tidy: we need at least one column with a character vector.
3. co2 is not tidy: it is a matrix instead of a data frame.
4. co2 is not tidy: to be tidy we would have to wrangle it to have three columns (year, month and value), then each co2 observation would have a row.

Write the number of the correct answer