What is present in $RNA$ instead of $Thymine$?

Purines found both in $DNA$ and $RNA$ are

Which of the following nitrogenous bases has a double-ring structure?

$A$ dinucleotide is obtained by joining two nucleotides together by a phosphodiester linkage. Between which carbons of the sugar of the nucleotides are these linkages present?

If the sequence of one strand of $DNA$ is written as follows:
$5'- ATGCATGCATGCATGCATGCATGCATGC-3'$
Write down the sequence of the complementary strand in the $5' \rightarrow 3'$ direction.

Which of the following statements are correct regarding $DNA$?
$(a)$ It is double stranded helically coiled.
$(b)$ The two strands are complementary and anti-parallel.
$(c)$ It has deoxyribose sugar and is acidic in nature.
$(d)$ It has only three nitrogen bases.