Given below are statements about the harmful effects of weeds on crop plants.
(i) They interfere while harvesting.
(ii) They help crop plants grow healthily.
(iii) They compete with crop plants for water, nutrients, space, and light.
(iv) They affect plant growth.
Choose the correct statements from above.

The correct option is B (i), (iii) and (iv)

Harmful effects of weeds on crop of plant are as follows:

• They interfere in harvesting.
  
• They compete with crop plants for water, nutrients, space and light.
  
• They affect plant growth.
  
• Presence of weeds increases the cost of agriculture and hinders the progress of work.
  
• It increases the irrigation requirement.
  
• They reduce the value of produce or otherwise adds the cost of cleaning.
  
• Some weeds when eaten (Cleome viscosa) by milch animals will produce an undesirable odour in the milk. At times death/disorder/deformity may occur. For example, Datura stramonium.

• The fruits and seeds of Xanthium strumarium and Achyranthes aspera entangle with wool which fetch lower prices.
  
• They harbour insect pests, pathogens and parasites.
  
• They reduce the value of the land.
  
• Presence of weeds will impair the purity of varieties by chance of cross pollination.
  
• Weeds cause health hazards to man and animals.
  
• Weeds cause allelopathic effect.
  

Therefore, the correct answer is option A.