Question

Before entering first grade, little mina used to love to read books. once school started, her teacher began a program to motivate her students to read. she began to give stars to those chidlren who finsihed a new book. as a result, mina no longer reads while she is at home. what has likely occurred?

Answer 1

I believe the answer is: Mina's intrinsic motivation decreased. 
Intrinsic motivation refers to the type of motivation that is based by internal rewards.
Things that could be considered as internal rewards would include: Personal interest/love , Ambition for the future,  desire to maintain good reputation , desire to be admired by others, etc.