问题
填空题
一根粗细均匀的电阻线，阻值为R，将其用拉丝机均匀拉长为原来的2 倍，再将其对折，则它的电阻值________R。（填“＞”，“＜”或“=”）
答案
=
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一根粗细均匀的电阻线，阻值为R，将其用拉丝机均匀拉长为原来的2 倍，再将其对折，则它的电阻值________R。（填“＞”，“＜”或“=”）
=
A. have
B. had
C. won't have
D. have had