In a geometric sequence, the common ratio \( r \) can be found by looking at the relationship between consecutive terms. Given the recursive definition of the sequence:
- \( a_1 = 56 \)
- \( a_n = 4a_{n-1} \)
From this, we can see that the relationship between term \( a_n \) and term \( a_{n-1} \) is defined by multiplying \( a_{n-1} \) by \( 4 \).
Thus, the common ratio \( r \) is \( 4 \).
So, the correct response is:
4