直肠、乙状结肠有病变时,除哪些情况外,可以行乙状结肠镜检查()
A.大便时出血
B.肛门狭窄
C.肛门直肠疼痛
D.妇女月经期
参考答案:B, D
_______ he exercises every day, _______ he is very healthy.
A.Though; /
B.Because; through
C.Because; /
D.Because; so
合力F,密度ρ,长度l,流速υ组合为无量纲的数是()。
A.A
B.B
C.C
D.D