A school club is raising money for a trip, and needs to reach $10,000. Their fundraising progress is modeled by the function

f(x) = 435 + 1200x, where x is measured in weeks.

What is the meaning of the coefficient 1200?
A) It is the amount they started with.
B) It is the amount still to be raised.
C) It is the amount which is left over.
D) It is the amount they raise each week.