A:①②
B:③④
C:②④
D:①④
The pupils in our school like reading after lunch, most of ________ seated on the grass unless it rains.
下列现象中,属于人口增长过慢造成的是( )
做空气中氧气含量测定的实验装置如图。下列有关说法正确的是( )
新疆气候干旱的主要原因是( )