A certain cluster of stars has the following characteristics:
• It is made up of a few thousand young blue stars.
• These stars are well spread out.
• The cluster seems to have no definite order or shape.
What could this cluster be?
A)
an open cluster
a spiral galaxy
a globular cluster
an elliptical galaxy

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 .