Hydrangea macrophylla is a species of plant with blue or pink flowers. Flower color in Hydranges macrophylla plants is thought to be determined primarily by soil conditions rather than by inherited differences. Which of the following will provide the most direct evidence that flower color in Hydrangea macrophylla is due primarily to soil conditions?

Actually question says which of the following where as there is no option given.

It is basically effect of environment on expression of gene for colour.

Explanation

pH of soil could be tested where hydrangea is being grown using pH meter. Colour of plant could be noted by growing at that particular pH keeping all other conditions as constant. It has blue colour in acidic soil and pink colour in alkaline soil.