Concept:Stirring (loosening) the topsoil of a vegetable bed breaks the hard crust that forms after watering or rain.
Explanation:I. Loose soil lets air into the root zone: improves aeration (correct).
III. Water soaks into loose soil instead of running off the crust: increases water penetration (correct).
IV. Stirring uproots young weeds: reduces weed growth (correct).
II. Any increase in the activity of soil organisms is only an indirect result of better aeration, not a main purpose of stirring. Also, every option with II leaves out I or III, which are clearly correct.
Answer:Option B (I, III and IV only)