Which of the following is the correct command to fade in an element over a three-second time period?

Which is valid?

Illustrate selecting a HTML element using its class:

Which is a syntactically valid jQuery command?

Which function does jQuery provide to remove whitespace from the beginning and end of a string?

What is the proper way to show an element?

Effects like show, hide, fadIn, and fadeOut can be called with no arguments, but can also take arguments for how long they should last. Which is NOT a duration argument supported by these functions?

What is tricky about jQuery's nth- filters (:nth-child, :nth-of-type, etc.) relative to other filters?

You want to work with AJAX using a Promise-like interface instead of nested callback functions. What jQuery API should you use?

When writing jQuery plugins, we often provide default options that may be overridden by the end user. What jQuery function is most useful for this purpose?

What is the difference between $('header').html() and $('header').text()?