What Is the Difference Between a Push View and a Pull

What is the difference between a push view and a pull view of supply chain processes?

A) In pull processes execution is initiated in response to a customer's order, whereas in push processes execution is initiated in expectation of a customer's order.
B) In pull processes execution is initiated in expectation of a customer's order, whereas in push processes execution is initiated in response to a customer's order.
C) In pull processes execution is initiated in response to a customer's order, whereas in push processes execution is initiated on the expectation of a supplier's order.
D) In pull processes execution is initiated in response to a supplier's order, whereas in push processes execution is initiated on the expectation of a supplier's order.