The Great Wall of China was originally built . ( ) A: from concrete B: from pounded earth covered with stone C: by stacking rocks on top of one another D: by sculpting it from clay

中国大学MOOC: Task: Read the article about a kind of fitness training called HIIT. Then choose the best explanations for some of the words and expressions. HIIT: Is the fitness scenes biggest fad doing more harm than good?1. High Intensity Interval Training (HIIT) has been the darling of the fitness scene for a few years now. Fundamentally, itinvolves repetitions of short bursts of intense, maximal effort exercise; usually for anywhere between 20 to 40 seconds.2. The theory behind HIIT is very appealing. By working out at your top level of exertion, you burn more calories in a short space of time than other workouts. Whats more, studies show that your metabolism stays in a heightened state for up to 24 hours after youve finished. And in practice, HIIT can have impressive results. Its an effective tool for increasing cardiovascular fitness, sculpting your physique and increasing metabolic rate. Hence why HIIT classes are popping up all over the place. People have become accustomed to turning up to a class with loud music and dark lighting,just like a night club – and leaving in the same state: barely able to walk.3. However ... I have a big bone to pick with HIIT, which is that theres often no focus on form or technique in these classes, even though its nowprescribed as the go-to form of exercise for everyone. Instead, the measure of a good HIIT sessions seems to be how destroyed you feel after a class. Its inevitable that problems arise from this all pain for gain approach.4. One issue is simply that people are doing workouts that theyre not conditioned for.There is no emphasis on flexibility, mobility or activation in manyHIIT classes; yet all are incredibly important in keeping the body fit and healthy as you age.5. Whats more, I regularly see people “smashing” multiple HIIT classes a day, 5-6 days per week. HIIT should not be done more than three times per week (at most), because it is so strenuous. It puts an incredible strain on your nervous system, joints and muscles; especially if you are overweight and unfit.6. The HIIT approach to exercise has gone OTT. Its enteringunsustainable territory.7. HIIT’s rise in popularity is symptomatic of what is wrong with the fitness industry as a whole: a brazen disregard of the fundamentals, and a detrimental “one size fits all” mentality. Having trained 100s of clients in my fiveyears as a personal trainer, the biggest issues most people have are a lack of flexibility, mobility and core strength, on top of muscle activation issues. All of the above can lead to chronic injuries and are further exacerbated by HIIT.8. My belief is that everyone should try to train like athletes do. I don’t mean the same training frequency and intensity as athletes, I mean the mentality and the approach. Having trained as a competitive sprinter for fouryears, I learned to take every aspect of my life into account: sleep, rest days, nutrition and weaknesses. I learnt to listen to my body. Some days I would wake up feeling tired and fatigued, so on those days I wouldn’t train hard.I would do something less intense and focus on recovery.9. Remember: burning calories isnt the be all and end all of fitness and good health. Yes, HIIT may burn more calories than any other form of exercise, but its no use if it leads to injury or illness.Overtraining is a real danger:it can ruin your immune system, cause insomnia, affect your appetite and release cortisol, which in turn can make you more likely to put on fat. ********************************************What does the word “fad” in the title probably mean?