Read the following statements and identify true (T) and false (F) amongst them:

(i) T–lymphocytes mediate the humoral immune response.

(ii) Mucus coating of the epithelium lining the respiratory and urogenital tract forms a physical barrier to specific immunity.

(iii) Bacteria–infected cells secrete proteins called interferons which protect non–infected cells from further infection.

(iv) An activated exotoxin called toxoid is used to induce active immunity to a toxin–causing disease.