The burden of proof in a suit or proceeding lies on that person who would fail if no evidence at all were given on either side.
(a) A sues B for land of which B is in possession, and which, as A asserts, was left to A by the will of C, B’s father
If no evidence were given on either side, B would b entitled to retain his possession.
Therefore the burden of proof is on A.
(b) A sues B for money due on a bond.
The execution of the bond is admitted, by B says that it was obtained by fraud, which A denies.
If no evidence were given on either side, A would succeed, as the bond is not disputed and the fraud is not proved.
Therefore the burden of proof is on B.