which sentence begins with a dependent clause?

a. When we go to school in the morning, we need to take our lunches and our backpacks
b. My dad is looking for his shoes while our dog is burying them in the garden
c. My friends and I are going camping today, and tomorrow my cousin is going to join us!
d. The children decided to play soccer in the park near their house

a. When we go to school in the morning, we need to take our lunches and our backpacks