Functions on tables

Which function can you use to retrieve the names of the rows of a data frame? Answer should be one word. 

Tip: try looking in the cheat sheet.

How to change the name of  the first column (mpg) of mtcars? Multiple answers are correct.

How to change the names of the third and fourth columns of mtcars? Multiple answers are correct.

Which argument do you to include in the merge function to include all the rows of D3 in the merged table?

Tip: check the documentation of merge().