To improve his English,he spends _______ one hour a day listening to English programmes. [ ]

A. at last

B. at least

C. at once

D. at all

下列属于专属管辖的案件有（）

A．离婚案件 

B．债务纠纷案件 

C．遗产继承案件 

D．合同纠纷案件