The correct answer is A. install_github(‘slidify’, ‘ramnathv’).
The other options are incorrect because they do not specify the correct package name or the correct GitHub user.
The package name is slidify, and the GitHub user is ramnathv.
To install a package from GitHub, you can use the install_github() function from the devtools package. The syntax is:
install_github(package_name, github_user)
In this case, the package name is slidify and the GitHub user is ramnathv. So, the command to install slidify from GitHub is:
install_github('slidify', 'ramnathv')