An advertisement designed to get mothers to buy a certain type of cereal should
a. use bright colors and cartoon characters.
b. feature teenagers playing video games.
c. focus on nutritional and cost values.
d. employ images of a serene and blooming garden.

The most logical answer is letter C--focus on nutritional and cost values. 

Women who have reached motherhood have already established a more mature and practical nature. Mothers who are trying to budget everything out, usually sees the cost value of an item. Also, mothers are naturally nurturing for their family and they want to purchase healthy items for their kids, making them look at a product's nutritional value. 

The bell is just a signal that the set time of the end of class is passing. the teacher lets you know when it's okay to leave.