Some herbicides are targeted at only monocots or only dicots.
a true
b false

of course the answer is true

Explanation:

All dicots are annual

i'm thinking (a) to keep sand in place; ////////////

explanation: a sand fence or sandbreak, like a snow fence, is used to force windblown, drifting sand to accumulate in a desired place. sand fences are employed to control erosion, sand dune stabilization, keep sand off roadways, and to recruit new material in desert areas.

a physical change is being made.