The correct answer is option A ("For example").
When supporting any kind of argument, presenting evidence is always a great way of strengthening the reasoning for backing up a certain position. The phrase "for example" is commonly found as a way to introduce or link factual evidence to a previously stated argument.
"Similarly" or "on the other hand" would be most commonly used to establish a comparisson; while "however" would point towards a counter-argument.
Hope this helps!
