Read the following statements and choose the correct option: Assertion (A): Desert plants like Opuntia have modified spines instead of regular leaves. Reason (R): Photosynthesis does not take place at all in the Opuntia plant.

Read the following statements with reference to the villi of the human small intestine: (i) They have very thin walls. (ii) They have a dense network of thin and small blood vessels close to their surface. (iii) They have large pores through which undigested food can easily pass. (iv) They are finger-like cellular projections. Identify the set of statements that correctly explains the features enabling the villi to absorb digested food effectively.

Read the following statements about diseases: (i) They are caused by pathogenic microorganisms. (ii) They are caused due to a lack of essential nutrients in our diet. (iii) They can be transmitted to another person through direct or indirect contact. (iv) They can be prevented by consuming a balanced diet. Which pair of statements best describes a 'deficiency disease'?