Step 1: Understanding the Question:
We must pick the correct statements about consumption as a component of aggregate demand.
Step 2: Check (A):
Ex ante means the planned or expected value of a variable. This is true.
Step 3: Check (B):
Ex post means the actual or realised value of a variable. This is true.
Step 4: Check (C):
Consumption does not change at a constant rate with income in the way the statement says, and the NTA key does not accept it. So (C) is false.
Step 5: Check (D):
A consumption function describes the relation between consumption and income. This is true.
Step 6: Match with the options:
(A), (B) and (D) are correct, which is option 2.
Final Answer:
Statements (A), (B) and (D) are correct, which is option 2 (as per the NTA final answer key).
\[ \boxed{\text{(A), (B) and (D) only}} \]