you should be careful when___(cross) the street in big citie

you should be careful when___(cross) the street in big citie You should BE careful when you cross the street in the big c when:you should be careful when _____ the street in big citi while___(cross)the street,you must be careful 连词成句：cross,be,the,when,careful,you,street You should be careful when you cross the m____ road . Be careful when you cross the street.为什么用cross而不用across? You must be careful when you cross the street.改为祈使句 be careful when you cross the street,or you may __run over b you must be careful when you cross the street.(同义句) You'd better be careful when you walk ( )[cross] the street. you must be careful when you cross the street中可以用if替代when吗