Critical Path Method

Given that Task D needs to be completed first before beginning Task E and Task F, that's 7 days. Task E requires 10 days and Task F requires 5 days. However, the question specified that Task E and Task F can be undertaken concurrently, which means they can be done at the same time. Thus, we don't add the durations of Task E and Task F together, we take the one that takes the longest to finish, which is Task E at 10 days. Therefore, the shortest duration to complete Tasks D, E, and F is the duration of Task D (7 days) + the longer duration of either Task E or Task F (10 days), which equals 17 days. The other options are not correct because they either overlook the fact that Task E and Task F can be undertaken simultaneously, or they miscalculate the overall time needed.

The best strategy while managing a construction project, especially in the face of an upcoming storm, would be arranging parallel tasks that do not depend on the foundation settling. This is because it would save time and ensure that the work continues while adhering to construction norms. It's essential to wait for the foundation to settle before erecting the walls to ensure the building's stability and lifelong durability. Starting to erect walls immediately after laying the foundation without waiting could lead to structural issues and is not considered good practice. Ignoring the storm and following the original plan in the sequential manner could also have a negative impact, potentially damaging the work that has been completed due to environmental conditions. Lastly, postponing the project until the storm is over might lead to unnecessary delays, especially if the storm lasts longer than expected. Therefore, conducting parallel tasks not reliant on the foundation settling is the most efficient and effective approach.

In the given scenario, tasks A, B, C and D are sequenced in order with each task taking 5 days to complete. Since task C was finished on the 15th day, task D should logically start on the 16th day because completion of a task denotes the readiness for the start of the subsequent task. Thus, the answer '16' is correct. The answer '15' is incorrect because it would imply that task D starts on the same day task C is finished, which is not typically how tasks are sequenced. Answers '17' and '18' are also incorrect as they suggest a delay in starting task D after completing task C, a situation not indicated in the given information.