Later in the Course, We Will Compare the Halogenation of Differently

Later in the course, we will compare the halogenation of differently substituted carbons, comparing reactions like the ones below. Which of the following statements is true about reactions A and B?

A) Both reactions have a positive heat of reaction ( $\Delta$ H^o)
B) Neither reaction has a positive heat of reaction ( $\Delta$ H^o)
C) Only reaction A has a positive heat of reaction ( $\Delta$ H^o)
D) Only reaction B has a positive heat of reaction ( $\Delta$ H^o)