JT-C系列机车信号采用双路接收线圈有什么意义？
参考答案：采用双路接收线圈后可实现JT-C系列机车信号完全的双套热备份。
When they awoke the next morning, they were surprised to find a ___ of fog floating in the air. [ ]
A. cover
B. blanket
C. piece
D. mixture
味觉发育的关键时期（）
A.2～3个月
B.3～4个月
C.4～5个月
D.5～6个月
E.6～7个月
