Using the data in the figure below, which defect should we study and try to reduce first (assume that correcting each defect for each vendor has the same cost to you per defect for all suppliers)?（　）
A．Incorrect invoice
B．Incorrect inventory
C．Incorrect test documentation
D．Cannot determine the correct answer from the available data
Supplier
Defect A B C D Total
Incorrect Invoice ││││ │ ││ 7
Incorrect Inventory ││││ ││ │ │ 9
Damaged Material │││ ││ │││ 8
Incorrect Test Doc │ │││ ││││ ││ 10
Total 13 6 7 8 34