The correct answers are BeginDialogAsync and PromptAsync.

BeginDialogAsync pushes a new dialog instance onto the dialog stack and begins that dialog immediately. You use it to start a waterfall or any dialog so that the new dialog runs on top of the current conversation flow and receives the next turn.

PromptAsync starts a prompt dialog by placing the prompt on top of the stack and awaiting the user response. In waterfall steps you commonly call a prompt so the prompt becomes the active dialog and then returns the collected result to the calling step.

CancelAllDialogs is incorrect because it clears or cancels dialogs on the stack instead of starting a new dialog on top. It is used to end or reset the dialog stack.

ReplaceDialog is incorrect because it replaces the current dialog with a new one rather than pushing a new instance onto the stack. Replace is used when you want to swap or restart the active dialog instead of stacking a new dialog above it.

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