Which two types of steel appear to have their properties combined in tempered steel?

Low and High Carbon Steel

Explanation:

Tempering Steel is to apply a process in the Steel to change its properties like ductility, hardness. Combining these two alloys resemble that:

The Low Carbon Steel, an iron-carbon alloy whose carbon content ranges from 0.4% to 0.03%,. It's malleable, and its use in industry is pretty common.  and the High Carbon Steel is another iron-carbon alloy whose carbon content ranges vary from 0.61% to 1.50%., hard to weld, bend and cut.

i believe the answer is a.

the answer is:  

line graphs show patterns in data with variables that change over time; whereas, circle graphs show data as parts out of a whole (such as out of 100%).