The process of establishing clear and achievable objectives, measuring their achievement, and adjusting performance in accordance, with the results of the measurement is called ______ .

A．strategic planning

B．alternative objectives inventory

C．management by objectives

D．contingency planning

回柱放顶时，必须每（）人一组，一人回柱放顶，一人观察顶板及支架周围情况，观察人除协助回柱外，不得兼做其他工作。严禁（）独自操作。