What is the difference between theme and authors purpose.

How can behavioral science be applied in improving public health? a.by tracking a disease to determine its sourceb.by creating promotions that improve health habitscboth by tracking a disease to determine its source and by creating promotions that improve health habitsd.neither by tracking a disease to determine its source or by creating promotions that improve health habits

Why did the author of "how to jump-start a car battery" choose to use this image?

Which of the following pronouns are singular