Most europeans make their living from what type of economic activity

Given: circle a externally tangent to circle b. how many possible common tangents to circles a and b can exist? 2 3 4

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 of these fragmental sedimentary rocks would most likely form farthest from the land?