文物是鲜活的历史。下列文物中最能反映商朝社会生活的是
A.兵马俑
B.司母戊鼎
C.竹木简
D.青花瓷
答案:B
He ______ be at home, because the light in his room is on.
A.must
B.can’t
C.can
D.might
假设模拟信号的频率范围是3-9MHz,采用频率必须大于______,才能使得到的样本信号不失真。
A.6MHz B.12MHz C.18MHz D.20MHz