The correct answer is A. sudden drawdown.
Sudden drawdown is the most adverse condition for stability of slope because it causes a decrease in effective stress and an increase in pore water pressure. This can lead to slope instability and failure.
Steady seepage is a less adverse condition because it does not cause a sudden change in effective stress or pore water pressure. However, it can still lead to slope instability if it is not properly managed.
During construction, the slope is often in a state of instability because it is not yet fully compacted. This can be a problem if the construction process is not properly managed.
Sloughing of slope is a type of slope failure that can occur when the soil on the slope becomes saturated and loses its strength. This can be a problem if the slope is not properly protected from erosion.
In conclusion, sudden drawdown is the most adverse condition for stability of slope because it causes a decrease in effective stress and an increase in pore water pressure. This can lead to slope instability and failure.