Final answer:
The 'add choice' in a Marketo Campaign send email flow step that allows for conditional actions based on criteria is 'Random sample'. It is used to select a subset of the target audience to receive an email, in contrast to other steps for delaying, modifying data, or removing leads from the flow.
Step-by-step explanation:
The student is asking about the "add choice" options in a send email flow step within a Marketo Campaign. The correct answer from the provided options is B. Random sample. In Marketo, an "add choice" step allows for conditional actions based on specified criteria. Random sample is one such choice, which can be used to send an email to a randomly selected subset of the target audience. The other options, such as Wait, Change data value, and Remove from flow, have different functionalities within a Marketo flow step. A 'Wait' step delays the progression of a lead through the flow, 'Change data value' modifies a lead's information, and 'Remove from flow' takes a lead out of a particular flow entirely.