Read the following paragraph and underline the topic sentence.
Whether work should be placed among the causes of happiness or among the causes of unhappiness may perhaps be regarded as a doubtful question. There is certainly much work which is exceedingly tiresome, and an excess of work is always very painful . I think, however ,that, provided work is not excessive in amount, even the dullest work is to most people less painful than idleness . There are in work all grades of enjoyment, from mere relief of boredom up to the profoundest delights, according to the nature of the work and the abilities of the worker. Most of the work that most people have to do is not in itself interesting, but even such work has certain great advantages.