领袖国家，是世界的文化旗手。引领世界，首先是（）引领。
A.经济引领
B.文化引领
C.军事引领
D.政治引领
参考答案：B
He is _________ about his chances of winning a gold medal in the Olympics next year.
A．optimistic
B．optional
C．optimal
D．obsessed
当酸和醇酯化时，如何选择缩合剂？
