子宫内膜结核常由何而来：
A．输卵管结核蔓延
B．宫颈结核蔓延
C．血行播散
D．卵巢结核
E．经淋巴系统蔓延
参考答案：A
They _____ have arrived at lunch time but the flight was delayed.
A．should
B．can
C．must
D．will
原核微生物与真核微生物各有哪些基因重组形式？
