A:L、R的单质与稀盐酸反应速率L<R
B:L与T形成的化合物具有两性
C:Q、T两元素的氢化物热稳定性Q<T
D:L、Q形成的简单离子核外电子数相等
When leaders of Chinese mainland(大陆)and Taiwan met in Singapore for ________ first time since 1949, President Xi said, "Today will be remembered in _________ history."