In this task, you are given a question and an answer, you would be asked to create the sentence based on the Question-Answer provided. It should be contained within the Question-Answer provided.

[EX Q]: Question: What is a measure that has both size and direction? Answer: vector
[EX A]: Vector is a measure that has both size and direction.

[EX Q]: Question: The outer surface of the heart changes from positive to negative during what? Answer: depolarization
[EX A]: The outer surface of the heart changes from positive to negative during depolarization.

[EX Q]: Question: What period starts after the baby is born, and the placenta is expelled from the body? Answer: postpartum
[EX A]:
The postpartum period starts after the baby is born, and the placenta is expelled from the body.