Select the number that can replace the question mark (?) in the following series. 25, 5, 49, 10, 81, 20, 121, ?

The series has two interleaved patterns: 25, 49, 81, 121 (odd-position terms, perfect squares increasing) and 5, 10, 20, ? (even-position terms doubling each time: 5×2=10, 10×2=20, 20×2=40). So the answer is 40.