单选题 A magnet is able to (picking up) a piece of steel or iron because (its magnetic field) flows into the metal, turning the metal (into) a temporary magnet, and the two magnets (then attract) each other.

A、 picking up
B、 its magnetic field
C、 into
D、 then attract

【正确答案】 A

【答案解析】将picking up改为to pick up。be able to do sth．为固定结构，表示“能够胜任某事”。此句的意思是“磁铁能够吸起一小块钢铁，是因为它内部的磁场流入金属中，使金属暂时转变为磁铁，从而两块磁铁彼此吸引”。