宪法修改的过程表明了我国的根本政治制度是( )
A:人民民主专政制度
B:人民代表大会制度
C:民族区域自治制度
D:社会主义制度
His family are worried about him because they haven't __________ letters from him for a long time.
Her father decided ________his holidays in Beijing.
九年级2班的同学在教师指导下用如图所示的实验装置进行“观察冰熔化”的实验.
— ______. I've got everything ready.