单项选择题

TEXT D
Analysts have had their go at humor, and I have some of this interpretative literature, but without being greatly instructed. Humor can be dissected, as a frog can, but the thing dies in the process and the innards are discouraging to any but the pure scientific mind.
In a newsreel theatre the other day I saw a picture of a man who had developed the soap bubble to a higher point than it had ever before reached. He had become the ace soap bubble blower of America, had perfected the business of blowing bubbles, refined it, doubled it, squared it, and had even worked himself up into a convenient lather. The effect was not pretty. Some of the bubbles were too big to be beautiful, and the blower was always jumping into them or out of them, or playing some sort of unattractive trick with them. It was, if anything, a rather repulsive sight. Humor is a little like that: it won’t stand much blowing up, and it won’t stand much poking. It has a certain fragility, an evasiveness, which one had best respect. Essentially, it is a complete mystery. A human frame convulsed with laughter, and the laughter becoming mysterieal and uncontrollable, is as far out of balance as one shaken with the hiccoughs or in the throes of a sneezing fit.
One of the things commonly said about humorists is that they are really very sad people-clowns with a breaking heart. There is some truth in it, but it is badly stated. It would be more accurate, I think, to say that there is a deep vein of melancholy running through everyone’s life and that the humorist, perhaps more sensible of it than some others, compensates for it actively and positively. Humorists fatten on trouble. They have always made trouble pay. They struggle along with a good will and endure pain cheerfully, knowing how well it will serve them in the sweet by and by. You find them wrestling with foreign languages, fighting folding ironing boards and swollen drainpipes, suffering the terrible discomfort of tight boots (or as Josh Billings wittily called them, "tite" boots). They pour out their sorrows profitably, in a form that is not quite fiction nor quite fact either. Beneath the sparkling surface of these dilemmas flows the strong tide of human woe.
Practically everyone is a manic depressive of sorts, with his up moments and his down moments, and you certainly don’t have to be a humorist to taste the sadness of situation and mood. But there is often a rather fine line between laughing and crying, and if a humorous piece of writing brings a person to the point where his emotional responses are untrustworthy and seem likely to break over into the opposite realm, it is because humor, like poetry, has an extra content. It plays close to the big hot fire which is Truth, and sometimes the reader feels the heat.
The author uses the example of the soap bubble blower to show that______.