B to E deserves it...BUT
To start with A, He's very OK looking at him and can stand for hours. For B, she's OK too and I don't think her pregnancy is heavy to the extend age won't bear the stand. For C, she's very old and can still work more than the old man (E) and the man with leg injury (D).

So my seat goes to the old man (E) because he's very very weak and looks like who need blood, water, food to survive and can collapse in a blink of an eye.