Answer: Option 'a' is correct.
Step-by-step explanation:
Reading comprehension makes children more efficient in making decisions and understand the actual meaning behind the line.
A factor that contributes to improved reading comprehension with age would be Children's knowledge of their world increases, so they understand more of what they read.
As they have improved their reading skills with age which makes them able to improve their vocabulary and understanding skills too.
So, Option 'a' is correct.