题目内容
（请给出正确答案）
[主观题]
If two trains are 120 miles apart and are traveling toward each other at a constant rate o
f 30 mph and 40 mph, respectively, how far apart will they be exactly 1 hour before they meet？
A．10 miles
B．30 miles
C．40 miles
D．50 miles
E．70 miles
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