单选题 采用DJ₆光学经纬仪在某站点观测一目标，盘左和盘右的读数分别为80°03'42"和279°56'54"。则该目标的竖直角大小为{{U}} {{/U}}。

• A.9°56'36"
• B.19°56'36"
• C.-9°56'36"
• D.-19°56'36"