A pizza parlor offers mushrooms, green peppers, and sausage as toppings for the plain cheese base. How many different types of pizzas can be made?

Step 1 ：We are given that a pizza parlor offers mushrooms, green peppers, and sausage as toppings for the plain cheese base. We are asked to find out how many different types of pizzas can be made.

Step 2 ：We can think of this problem as a combination problem. Each topping can either be chosen or not chosen, so there are 2 choices for each topping.

Step 3 ：Since there are 3 toppings, the total number of combinations is \(2^3\).

Step 4 ：However, this includes the case where no toppings are chosen, which is just the plain cheese base. So we need to subtract 1 from the total.

Step 5 ：Doing the calculation, we find that the number of combinations is \(2^3 - 1 = 7\).

Step 6 ：Final Answer: The number of different types of pizzas that can be made is \(\boxed{7}\).