在如图所示的竖式里,四张小纸片各盖住了一个数字.被盖住的4个数字的总和是( )
A:14
B:24
C:23
D:25
My friends thought they had made things very smooth for me, but I felt there was still much to ________ with.
某密闭容器内盛有氧气和氮气的混合气体,采用燃烧法除去其中的氧气,且不能混入新的气体,最好采用的可燃物是( )