### 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: So you're sure to ask: Why is the shelf life one year for bags and two years or more for cans?
### Errors: There is a minor error at "bags".

### 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?