Which of the following sentences expresses a certainty？
A. In England, traffic must keep to the left.
B. All men must die.
C. You must be hungry after your long walk.
D. You must be joking.
试述理解“津血同源”和“汗血同源”的机理及其临床意义。
A: Father, you promised. B: Well,_____!
A. so I did
B. so did I
C. so I do
D. so do I
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