Hi Masa - there are probably two ways to achieve this, which may work in different use cases.
1) Utilize multiple dropdowns.
You can place several dropdowns in your kintone app, that have different options inside. I'm not sure from your question, what conditions are changing the Drop-down options, but you can hide/show fields depending on particular conditions using:
2) Create a dropdownfield on a Space
This solution does not require you to set up a drop-down field in your app settings.
To retrieve the space element use:
var el = kintone.app.record.getSpaceElement('spaceID');
where "spaceID" is the ID you can give to the space.
When a user selects an option from the drop-down list, make sure to insert the same value into a single-line text field (that the user cannot see). This will enable kintone to hold that data within the record.
Solution 2 would be a bit harder to implement, but it would allow data to be stored into one field (rather than several) which would probably help when you try to create graphs afterwards around this data.
Hope this has helped.