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.
To hold back an expression of anger.
Explanation:
Dear friend
How are you doing today I hope all is well with you and your family am writing this letter to you to tell you about my upcoming birthday celebration.
I going to have a great birthday celebration at the biggest event center in the Victoria Island and all my friends and family are going to be there so pls i beg you to attend the party
Your's sincerely
Dear friend
<span>B. Schools should move away from standardized testing because tests often do more harm than good.
It stays on the topic of testing and is simplistic.</span>