Biochemistry II. Please help answer hw question with clear explanation.

A researcher adds 14C-labeled glyceraldehyde 3-phosphate (GAP) to a yeast extract. After a short time, she isolates fructose 1,6-bisphosphate labeled substantially with 14C at C3 and C4. Where was the 14C label in the starting GAP located? C-3 C2 and C3 C-2 C-1 Where did the second 14C label in fructose 1,6-bisphosphate come from? The labeled GAP becomes dihydroxyacetone phosphate (DHAP) through triose phosphate isomerase activity. \begin{tabular}{|c|} \hline[114C] \\ \hline[314C] \\ \hline[214C] \\ \hline \end{tabular}