The equation a + bx ® ax + b is the general equation for a
a.
double-replacement reaction.
c.
replacement reaction.
b.
decomposition reaction.
d.
combustion reaction.

in cartography, a contour line (often just called a "contour") joins points of equal elevation (height) above a given level, such as mean sea level. a contour map is a map illustrated with contour lines, for example a topographic map, which thus shows valleys and hills, and the steepness or gentleness of slopes.

explanation: