（英语）句型转换 急用!Bob said he hadn't been able to pass the maths t

（英语）句型转换 急用!
Bob said he hadn't been able to pass the maths test.(保持原句) Bob said he had（）（）pass the maths test.He suddenly saw a little boy in front of his car.(保持原句) A little boy （）his .（） The watch is fifteen dollars cheaper than before.(保持原句) They （）the price for that watch （）fifteen dollars.Air pollution is the most serious kind of problem here.(保持原句) Air pollution is a （）serious kind of pollution than （）other kind of problem here..I haven't met my elder brother for a year.(保持原句) It （）a year （）I met my elder brother.Mary sings best in our class.(保持原句)No one （）in our class sings so（） as Mary.Mr.Smith told us that we mustn't litter.(保持原句)Mr.Smith told us （）（） litter.Her sister working in her office now.(保持原句)Her sister is busy （）in her office now.Why not start the work right now?(保持原句)You （）（） start the work right now.