### Chinese: 那么大家肯定会问：为什么袋装保质期是一年，而听装的保质期是两年或更长呢？
### English: Then you must ask: Why is the shelf life of the bag is one year, and the shelf life of the can is two years or more?
### Errors: There is a major error at "must". There is a major error at "is". There is a major error at "of the bag is". There is a major error at "can".

### Improved English: Then you may ask: why is the shelf life of milk powder one year in bags and two years or longer in cans?