Final answer:
A prime minister can become the prime minister for the third time through re-election or by calling for snap elections depending on the country's political system.
Step-by-step explanation:
A prime minister can become the prime minister for the third time through various means depending on the country and its political system. For example, in the case of Benazir Bhutto, she became the Prime Minister of Pakistan for the third time after running in elections and being reelected in 1993. However, charges of corruption led to her being removed from the position a second time in 1996. In some countries, like the United Kingdom, the Prime Minister can call for snap elections at will, which allows them to potentially be reelected for a third time.
In summary, a prime minister can become the prime minister for the third time through re-election or by calling for snap elections depending on the country's political system and the circumstances surrounding their tenure as prime minister.