Steel is an alloy composed ____________ of iron and carbon.

Steel is an alloy composed ____________ of iron and carbon.
A、primarily
B、traditionally
C、carefully
D、partially
【正确答案】：A
【题目解析】：primarily主要地；traditionally传统上地；carefully小心地，谨慎地；partially部分地。该句的意思是“钢铁主要是由铁和碳构成的一种合金”，故答案为A。