如果市场上所有顾客在同一时期偏好相同，对营销刺激的反应也相近，宜实行无选择性市场策略。
参考答案：对
—Has Sam finished his report?
—I have no idea. He _______ it in his office the whole morning.
A．writes
B．has written
C．will write
D．was writing
对承担涉密武器装备科研生产任务的企事业单位，实行保密资格（）制度。
