For $H_{3}P{O}_3$ and $H_{3}P{O}_4$ the correct choice is:

$H_{3}P{O}_3$ is a dibasic acid as it has 2 number of replaceable $OH$ groups(Dibasic) attached to phosphorous. The oxyacids of phosphorous are reducing agents.

$H_{3}P{O}_3$ is a good  reducing agent than $H_{3}P{O}_4$ . The reducing nature of these acids is based on the no of hydrogen atoms bonded to the central metal atom. As more number of H attached to phosphorous more is its reducing nature. In the case of $H_{3}P{O}_3$, there is one $P-H$ bond which is responsible for it's reducing character whereas there is no such bonding in case of $H_{3}P{O}_4$.

Hence option $A$ is correct.