问题补充:
Tom was walking along the riverside when he heard someone calling him from behind. He turned around found nothing.
A. but
B. and
C. so
D. or
答案:
(答案→)A. but
B. and
C. so
D. or
解析:句意:Tom 正沿着河边散步这时他听到有人从后面喊他。他转过身来,但是什么也没发现。根据句意可知,此处应表示转折的关系。and和,表示承接;so 因此,所以,表示因果;or 或者,表示选择。故选A。