Guard cells help in

Stomata in plants open due to the ............ .

Out of the following, which one is the most common type of transpiration?

When do the stomata close?

Due to low atmospheric pressure,the rate of transpiration will

$A.$ In dry atmosphere,the relative humidity is low,so the rate of transpiration increases.
$B.$ Slow breeze promotes the rate of transpiration.
$C.$ $ABA$ promotes transpiration.
$D.$ $A$ high salt concentration in soil water increases transpiration.