A、<span style="line-height: 29px; font-family: 宋体;">收集资料 </span>
B、<span style="line-height: 29px; font-family: 宋体;">选择课题 </span>
C、<span style="line-height: 29px; font-family: 宋体;">提出假设 </span>
D、<span style="line-height: 29px; font-family: 宋体;">制定方案</span>