Test analysis: when there is a concentration difference between the liquid inside and outside the plant cell, the plant cell will absorb water or lose water; When the concentration of external fluid is greater than that of intracellular fluid, it will absorb water; When the concentration of exogenous solution is less than that of intracellular solution, the soil solution in saline-alkali soil contains more saline-alkali soil, and the concentration of soil solution is also higher. Therefore, the main reason why plants in saline-alkali soil can strongly absorb water from the soil is that the concentration of root hair cell solution is high, so plant cells will absorb water, so B is chosen.