—In the morning.
A:What time
B:When
C:What
D:Where
①聚丁二酸乙二醇酯(PES)是由两种单体通过____反应(填反应类型)制得的.形成该聚合物的两种单体是____.
②这两种单体相互之间也可能形成一种八元环状酯,请写出该环状化合物的结构简式____.
We study Chinese, English and some _______ subjects.