26. B (Spending long amouts of time in space makes bones and muscles weak)
27. D (scientsts use space station... in space, dòng 2-3)
28. C (The first US space staion, Skylab, was launched in 1973)
29. D (The space shuttle...together, dòng 1-2 đoạn 2)
30. C (dòng cuối)