Weeds affect the crop plants by
(a) killing of plants in the field before they grow
(b) dominating the plants to grow
(c) competing for various resources of crops (plants) causing low availability of nutrients
(d) all of the above
In the cultivated fields of farms, some undesired plant species grow along with desired crops. These undesired plants are called weeds. These weeds start resources like space, water, light, and nutrients for the crops. The weeds suppress the growth of crops by causing low availability of nutrients. Enormous growth of weeds could kill the plants in the field before they grow.
Hence, the correct option is D.