消化性溃疡的主要症状是（）。
A.恶心、呕吐
B.上腹疼痛
C.呕血黑便
D.嗳气、反酸
E.厌食、消瘦
参考答案：B
A good teacher ought to be familiar ________ teaching skills.[ ]
A. to
B. with
C. of
D. at
COSPAS-SARSAT is intended to be used for（）.
A.distress alerting
B.locating 406mhz EPIRBs
C.storing distress signal
D.A and B
