在工程网络计划中，工作M的最迟完成时间为第25天，其持续时间为6天。该工作有三项紧前
题型：单项选择题
问题：
在工程网络计划中，工作M的最迟完成时间为第25天，其持续时间为6天。该工作有三项紧前工作，它们的最早完成时间分别为第10天、第12天和第13天，则工作M的总时差为( )天。
A．6
B．9
C．12
D．15
题型：单项选择题
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