When might engineers use a topographical map?

In the diagram below dab and dac are adjacent angles

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

All of the following came out of china and were exchanged along the silk road, except a. papermaking b. block printing c. buddhism d. compasses select the best answer from the choices provided a b c d