开垦土地
参考答案：
是指以垦殖为目的开发土地，即开垦荒地为耕地用于农作物的种植。
主系统吹扫时，N为什么经缓冲罐高点放空阀排至大气？
--- Did you ask the guard _______ happened?
--- Yes, he told me all _______ he knew.
A．what; that
B．what; what
C．which; which
D．that; that
