ANSWER is 'sank'. In the given QUESTION 'yesterday' is a keyword. It denotes the past time. Therefore, the second form of the verb should be used. We know that 'sank' is the second form of 'sink'. Correct Answer: Sank. The simple past tense TALKS about a completed action in a time before now. The simple past is the basic form of past tense in English.The time period of the action can be in the recent past or the distant past and the duration of the action is not IMPORTANT. Example: John Cabot sailed to AMERICA in 1498.