because humans are not perfect and have their own prejudices and bias so no document will ever be "perfect"
Answer:
the first one, when it says when we were there, it's missing a comma behind when
By explaining problems and giving solutions! this is the best fit because the other two might make sense at a first glance, but only explaining problems and solutions would be an effective way to teach people how to set up an aquarium by giving them examples of what to do and what not to do whereas the others are just him talking about his aquarium.
Adverbs are words that are used to modify or qualify the verb, adjective and sometimes another adverb. From the sentence above and from the choices given, the word that is not an adverb is the word because. Thus, the answer is letter D.