Why does a compass needle point north?

Gemstones are commonly found in pegmatites, which are igneous rocks that are a. exceptionally mafic b. exceptionally coarse grained c. exceptionally fine grained d. extrusive, forming from lava

Which of the following areas has the highest population density?

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