The weight of a sequence a0, a1, ..., an-1 of real numbers is defined as a0+a1/2+...+ aa-1/2n-1. A subsequence of a sequence is obtained by deleting some elements from the sequence, keeping the order of the remaining elements the same. Let X denote the maximum possible weight of a subsequence of a0, a1, ...,an-1 and Y the maximum possible weight of a subsequence of a1, a2, ...,an-1. Then X is equal to

• A. max(Y, a0+Y)
• B. max(Y, a0+Y/2
• C. max(Y, a0+2Y)
• D. a0+Y/2