Invent challenges. A hundred years ago, pi

问题：

Invent challenges. A hundred years ago, pioneer psychologist William James declared that humans use only a (67) part of their potential. All too many of our tasks are (68) or tedious. Then the brain operates almost on (69) The result can be careless mistakes or dragged-out drudgery because we can get with it.
The perfect state of flow, Csikszentmihalyi explains, (70) when our skills exactly measure up to the challenges confronting us. (71) , says Csikszentmihalyi, the way to get a dull but simple job done easily is to make it harder. Turn a boring task into a challenging game, so that you (72) all your potential. Invent rules, (73) goals, (74) yourself against a clock. This increased challenge may be what pushes you into your (75) .
I was once asked to write an introduction to a (76) of articles on lawsuit. Words came slowly as I (77) away at a topic that didn’t inspire me. I made (78) trips to the coffeepot. Then the magazine’s art director phoned to say he’d created an eye-catching (79) for the article, drawing a gavel (槌) bent into the letter J. Could the first word of the article begin with J
I not only accept the challenge, but added one of my own: Could every paragraph begin with J Using such words as Justice and Jurisprudence (法学), I managed nine paragraphs. By (80) my attention, the contest sped up the task.
Talk to yourself. As you (81) that drip irrigation system in your rose bed, tell yourself, "The line to the hose bib goes here. About six feet, then the first emitter (喷嘴)..." Verbalizing keeps your mind on the task, (82) the steps you’re taking, and reminds you of what needs to be done.
Self talk can also serve as "white noise," taking your mind off (83) stimuli. A young ski racer, (84) by spectators and blowing snow, was having a disappointing competition when his coach pulled him (85) . "Look ahead," the coach said, reminding the skier to (86) on the gates ahead as he skied the ones before. Repeating the phrase like a spell (咒语): "Look ahead, look ahead, look ahead"—the skier focused his attention and won a medal.

A．variable

B．numerous

C．variant

D．abundant