Biology Quiz Questions Genetics and RNA... Why are these correct

I took a few bio quizzes recently and do not know/understand why the answers are what they are. Hopefully someone will be able to help me to better understand these topics.

First, this was a True/False Question: A child with type O blood cannot have a parent with type AB blood. I said "False" but it was in fact True. Can someone explain why this is?

Second: These were from a matching section. The possible answers were: a)tRNA, b)mRNA, c)rRNA. I think I'm having trouble understanding what each does specifically. Correct Answer in parenthesis...
1)Carries genetic information or Codons (B)
2)Transports Amino Acids (A)
3)Long Linear Molecule (B)
4)Globular, reads the codes or codons (C)
5)Highly coiled, and contains the anticodon (A)

I actually got only 1 wrong from that section, but that was purely from guessing. Can someone give me an explanation into rRNA, tRNA, and mRNA so that I can understand the role of each?

First question:
Technically, a child with type O blood can have a parent with type AB (via H substance). However, in the scope of introductory genetic classes, the answer would be True because a parent with AB blood type has an A allele and a B allele. That means that the child will receive either an A or a B allele from that parent. If the child receives an A allele, the child may have AB, AA, or AO blood type. If the child receives a B allele, the child may have AB, BB, or BO blood type. In order to have O blood type, the child must receive an O from each parent, since O is recessive. Since you can only get A or B from one of the parents, it is not possible to get two O's.

Summary:

Parent 1: AB
Parent 2: ??
Possible children: A?, B?
Child with O blood type: OO

A? and B? does not make OO.

Second question:
-mRNA is the messenger RNA. It carries the information from DNA and is used as a message to create proteins.