A:one needs to have profound knowledge
B:profound knowledge is important
C:profound knowledge is a must
D:it is required that one has profound knowledge
图示截取人体部位连通的三种血管的片段,其中的血液依次流经( )
有x支球队参加篮球比赛,共比赛了45场,每两队之间都比赛一场,则下列方程中符合题意的是( )