a) DNA and RNA are both formed by a sugar phosphate backbone and nucleotides. They share the bases Adenine, Guanine and Cytosine.
b) In RNA the base Thymine is replaced by the base Uracil, so for RNA Adenine pairs with Uracyl and not with Thymine.
The sugar phosphate backbone of DNA is formed by desoxyrobose sugart while the backbone of RNA is formed by ribose sugar.
DNA has a double stand while RNA is single stranded.
c) The base Thymine always pairs with the Base Adenine in both DNA and RNA.
You can see it in the picture where the green lines (Thymine) are always paired with a red line (Adenine)