Which property of $DNA$ double helix led Watson and Crick to hypothesise semiconservative mode of $DNA$ replication? Explain.

(N/A) Watson and Crick observed that the two strands of $DNA$ are anti-parallel and complementary to each other with respect to their base sequences.
This specific property of base pairing led them to hypothesize that $DNA$ replication is semiconservative.
It implies that the double-stranded $DNA$ molecule separates,and each separated strand acts as a template for the synthesis of a new complementary strand.
As a result,each new $DNA$ molecule consists of one parental strand and one newly synthesized daughter strand.
Since only one parental strand is conserved in each daughter molecule,this process is known as the semiconservative mode of replication.