In the following passage, some words have been deleted. Read the passage carefully and select the most appropriate option to fill in each blank.
Smoking is the leading cause of death from bronchogenic carcinoma of the lungs, as well as a cause of death from larynx, oral cavity, oesophagus, bladder, kidney, pancreas, stomach, uterine cervix and coronary heart disease. Nicotine is the (1)_______ addictive component of tobacco smoke. The additives, too, cause (2)_______ to the body; for example, ammonia can result in a 100-fold increase in nicotine's (3)_________ to enter the nose. Nicotine's 'kick' can be amplified by levulinic acid, an additive used to conceal the nicotine's harsh taste, by (4)________ the binding of nicotine to brain receptors. More than four thousand compounds and more than forty known carcinogens are found in cigarette smoke. Tobacco smoke has been well (5)______ as a proven carcinogen and cancer cause for many years.
Select the most appropriate option to fill in blank no. 4.