For the given blank in the sentence, the words "whet" and "burden" are not feasible to be used. That leaves us with just the other two options- "affect" and "effect".
Now, both of these words are easily confused. They are homophones which means they have the same sound but differ in their spellings and meanings. So, the word "affect" means "to cause", "to have a impact" or "to change" while "effect" means the result of an action.
Therefore, the whole sentence will be-
<em>One </em><u><em>effect </em></u><em>of global warming could be the creation of superbugs.</em>
