亚洲东北以_______海峡与北美洲为界，西南以_______运河与非洲为界。
白令；苏伊士
______, I lost heart in English learning, but my teacher often said to me, “Keep on working hard; you’ll succeed _______.”
A．At a time; in time
B．At a time; on time
C．At one time; in time
D．At one time; on time
小麦白粉病在叶片上开始发病的症状表现为（）。
A、水浸状斑点、白霉点
B、水浸状斑点、白粉霉点
C、白色小霉斑
D、白色粉霉层
