问题补充：
About of the workers in the factory were born in the .
A. two-thirds;1970
B. two-thirds;1970s
C. two-third; 1970
D. two-third;1970s
答案：
A. two-thirds;1970
(答案→)B. two-thirds;1970s
C. two-third; 1970
D. two-third;1970s
解析：表示几分之几，应该是基数词—+序数词的复数（单复数形式要根据基数词来决定），而in the +年后接s，故选答案B
