If two groups of plants have different soil types how will this affect an investigation of light?

Correct answer: Soil may also affect the result

The direct answer is B: soil may also affect the result. The investigation is supposed to test light, so the soil type should be kept the same in both plant groups. Step by step, light is the independent variable, plant growth is the dependent variable, and soil type is a possible controlled variable. If one group has different soil, that soil may change water retention, minerals, drainage or root growth. Then a difference in plant height cannot confidently be attributed to light alone. Option B is correct because soil becomes a confounding factor. Option A is wrong because adding another difference does not make the light effect clearer; it makes interpretation harder. Option C is wrong because different soils can cause different growth. Option D is wrong because the dependent variable, such as plant height, does not disappear; it may simply be affected by more than one factor. Memory cue: for a fair test, change one factor and keep other important conditions alike.