HELP QUICK PLEASE! What determines the boundaries of a watershed?

A.
elevation features like hills, mountains, and ridges
B.
placement of cities and urban sprawl
C.
man-made boundaries like drainage ditches and reservoirs
D.
average annual rainfall in the area

How many copies of genes do gametes have?

The images show two species of tree frogs in a particular region. the gray tree frogs are adapted to the trees of the woodlands, while the green tree frogs can survive in woodlands or grasslands. the gray frog was abundant in the woodlands. because of climatic changes, most of the trees in the region died, and the woodlands changed to grasslands. in such a case, the . the gray tree frog is closely related to the green tree frog genetically, but they have different mating calls. this suggests that speciation occurred because of .

All of these things can block a bronchus and cause collapse of a lung except