【单选题】The main cause that makes Africa highly-concerned internationally is
A.
the abundant underground natural resources.
B.
the cheap labor force in manufacturing industries.
C.
the solid faith in numerous chances of doing business.
D.
the barrier-free trade policies made by the government.
【单选题】Even as (), he made several wonderful inventions.
【单选题】—Why is surface subsidence most serious in this area? —Because large quantities of underground water______.
【单选题】The second paragraph tells us ______
A.
underground is convenient
B.
the advantages of underground
C.
we can have good food underground
D.
you can spend the night underground
【简答题】溢流坝的溢流面由顶部的()、中间的()、底部的()组成。
【单选题】74LS193的置数法选用( )门电路控制?