单选题
Why is transition difficult?
A、
Because transition requires money and time.
B、
Because many manufacturers are unwilling to change their equipment.
C、
Because research on new materials is very difficult.
D、
Because it takes long time.
【正确答案】
A
【答案解析】
[解析]由短文最后一段中的“And that transition could prove difficult，for switching requires lengthy research and investment．”可知答案为A。故应选A。
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