A-A+
A．They aren't sure how these cells work.B．They
问题详情
A．They aren"t sure how these cells work.
B．They have difficulty identifying these cells.
C．They"ve found similar cells in other species.
D．They"ve learned how to reproduce these cells.
参考答案
正确答案：A
解析：观点题。从对话中In fact，the scientists who study human bones don't completely understand it yet．，我们可推知科学家对此也不是很确定，A正确。
