Assume that Prover have $n$ pedersen commitments ($V_{a_1},V_{a_2},\cdots,V_{a_n}$ where $V_{a_i}=G \cdot a_i + H \cdot r_{a_i}$) of $n$ elements $a_1,a_2,\cdots,a_n$. The Prover have another element $\theta$.
The verifier is provided with these $n$ pedersen commitments ($V_{a_1},V_{a_2},\cdots,V_{a_n}$) and $\theta$.
How can the Prover prove that the sum of $\textbf{only one}$ subset of these elements $a_1,a_2,\cdots,a_n$ can equal to $\theta$ and don't reveal these elements to verifier? (the size of this set is a constant witch smaller than $n$)