下列与人类社会生产力逐步提高相适应的人口增长模式,正确顺序是[ ]
A.原始型、传统型、现代型
B.传统型、原始型、现代型
C.原始型、现代型、传统型
D.传统型、现代型、原始型
答案:A
All the students were excited that English would become an optional course.
A.hearing
B.to have heard
C.heard
D.to hear
烧结点火的目的在于将混合料固体燃料点燃,向料层提供热量,借()的作用,继续烧结。