我国陆地领土面积排世界第三位,仅次于 [ ]
A.俄罗斯和美国
B.俄罗斯和加拿大
C.加拿大和美国
D.美国和巴西
答案:B
心脏杂音产生机制如何?
What is the point the speaker is trying to make about technology development a. A mature technology requires less innovation. b. Technical evolution is close to maturation in certain fields. c. New types of energy are expected to mature in the near future. d. Nanomaterials or photonics and carbon nanotubes are environmentally friendly.