Which of the following regulates blood pressure and heart rate?

An organic compound containing $C$ and $H$ has $92.3 \%$ of carbon. Its empirical formula is:

If $\alpha, \beta, \gamma$ are the roots of $x^3+2x^2-3x-1=0$,then $\alpha^{-2}+\beta^{-2}+\gamma^{-2}=$

Which of the following plants are used as green manure in crop fields and sandy soils?

The ratio of the mass percentages of $C$ and $H$,and $C$ and $O$ of a saturated acyclic organic compound $X$ are $4:1$ and $3:4$ respectively. Then,the moles of oxygen gas required for the complete combustion of two moles of organic compound $X$ is:

$A$ column of water within xylem vessels of tall trees does not break under its weight because of