Which of the above improve overall steam power plant efficiency?

Question

Consider the following:    

1. Superheater

2. Economizer

3. Air pre-heater

4. Condenser

Which of the above improve overall steam power plant efficiency?

a. Only 1, 2 and 3       b. Only 2 and 3

c. Only 1 and 4           d. 1, 2, 3 and 4