Answer:
It is considered to be a bit disrespectful to write to a teacher in an unprofessional, casual manner, the way you would a friend because you aren't close on a personal level. Of course it depends on the teacher and subject of the letter/email/etc. as well.
Answer:
<em>They are similar because they both one topic that are alike</em>
True. they help you understand new vocabulary and that also help you understand what that sentence is about.
