单选题
One problem that has not yet been solved, it seems, is that ______.
A、
a prototype has not yet been accepted
B、
financial backing is not available
C、
the machine will need fire-resistant sensors
D、
the machine would not work if the ventilation was overwhelmed
【正确答案】
B
【答案解析】
根据最后一段Piatti is now looking for financial backing to build a prototype可以判断，目前为止还没有找到财力支持。
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