这题型我第一次遇到，是一个文章里抽些语句考语法，后面再要你阅读理解，老外的思维真怪。。。=================================== Keeping a swimming pool clean can be more work(than/if/for/but)you might imagine . It involves removing things that you can see (easy/ate easier/easily/be easily)such as leaves and other debris,and things that are harder or impossible to see(as example/such as/like as as for)body oils.perspiration,harmful bacteria,and algae.Pool experts have determined the proper levels of chemicals that must(maintain/be maintained /have maintained/be maintaining)in pool water to protect the swimmers from infection and the equipment(by/from/for/of)corrosion and damage.Chlorine kills harmful organisms, but it won't work properly if the alkalinity of the water is too(low /below /under/ beneath) If the calcium content of the water is inadequate, the water will leach calcium from the walls of the pool,(have weakened/is weakening/weakening /weakens)them. what is the main topic of the passage?How chemicals destroy harmful substancesHow to remove debris from a poolUse of chemistry in everyday lifeFactors that affect pool maintenanceWhat happens if the level of calcium in the pool water is not high enough?The water takes calcium out of the sides of the poolThe level of alkalinity decreasesThe water in the pool will turn greenAlgae will grow on the walls of the poolThe word"determined" in line 32 is closest in meaning tohinred atnotifiedfigured outwonderedChlorine is added to pools in order todestroy infection-causing agents in the watermake the walls of the pool strongeradjust the alkalinity levels of the waterkeep the water from drying out the swimmers'body oilsDead tree limbs and twigs that fall into a swimming pool would be considered examples ofharmful bacterialeachingdebrissources of calcium

阿。。。我都看不懂。。。221.210.18.*的大哥，能帮我看下不