See many compilers take some kind of shortcut to comment out blocks of code. The default compilers use something like command or control and a single quote to comment out selected lines of code. In RStudio it is Command or Control+/. Check-in your editor.
In the case of the Mac RGUI, the command is command-option ' but for the Rstudio, you just have to press Control + Shift + C again.
If you are a beginner and want to know more about R then do check out the R programming tutorial.
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