填埋法使用的填埋坑内，微生物利用硝酸根和硫酸根作为氧源，产生硫化物、氮气和二氧化碳，

根据句子意思，用方框内所给词的适当形式填空，每词只能用一次。（5分）

health       die       possible      develop     invent

小题1:China is a                  country.
小题2: Philip went into his room and                 (shut) the door behind him.
小题3:Noisy conditions may make people                 .
小题4:One of the greatest                  in 20th century is light.
小题5:It’s                  for him to solve the problem, because it’s too hard.