Premise: from 1973 to 1976, c's consumption increased by 3.4%, sales of t rose 18% and total population: 5%
There is no assumption. and we have to find the conclusion / interference
A) nothing is mentioned about profit / prices. So we can't conclude
D) similar to A.
E) we just know that c's consumption and t's consumption increased. whether there was a switch or not, we don't know

C) first of all non-smokers.. does that include only c or only t or both.. ?
may initially only 1 person out of 1000,000 consumed c. then even if c's consumption increased by 3.4%, as population increases by 5%, proportion of non-smokers will increase

B) let 100 people and x people consumed c. then per capital consumption in 1973 = x/100
now 1.034x and 105 persons. thus per capital consumption in 1976 = 1.034x/105 = .98x/100
as this is less than x/100, thus B is true...

'73 - smokers 100 tobacco 100 non smokers 100 total population 300
'76 - smoking 103.4 tobacco chewing 118 non smokers 115/or more total population 315

thus this clearly indicates that both smoking and T chewing has increased,while non smokers population has increased too.
B clearly fits in.

premise - statement mentioning the increase percentages for smoking,chewing and population.
conclusion - B.