What must two objects have in order for gravitational force to act on them?

Landmasses on a flat map look distorted because

Some gamma ray bursts are hypothesized to come from mergers of neutron stars or black holes. if this hypothesis is correct, what else should we in principle be able to detect from such mergers? a. gravitiational waves b. x-ray bursts c. significant disruption of gas thousands of light-years away in the surrounding galaxy d. an "afterglow" of bright visible light, lasting for weeks

Which describes italy’s mediterranean climate? a. moist in the summer and dry in the winter b. mild and wet all year round c. cool in the summer and warm in the winter d. hot in the summer and mild in the winter