Bronchial smooth muscle relaxation and vascular smooth muscle constriction are caused by the direct actions of the:

a axis of a graph is a color or shade so we can all go outside and have a party so we can eat   some grilled cheese sammiches and broccoli and have some ugly fun times

i don't know why i put this, i know its not the i was just bored : p

delete this answer while you can

since there are no options posted i'll give you a few examples.

a dolphin's flipper, bird's wing, cat's leg.