BCD is the correct answer. Please refer salesforce article:
https://help.salesforce.com/s/articleView?id=sf.notes_on_changing_custom_field_types.htm&type=5

The answer is BCE. As per the link given by others, it can cause data loss if we change from currency to any other type but not always. D implies data is always lost if we covert to currency, therefore D is incorrect.

BDE

A. Rollup summary fields will stop calculate if Master Detail is changed to lookup - After you have created a roll-up summary field on an object, you cannot convert the object's master-detail relationship into a lookup relationship.
B. No data is lost when converting Text to auto number - Changing to Auto Number from any type except Text can cause data loss
C. No data is lost when changing Picklist to Multipicklist - Currently defined picklist values are retained when you change a picklist to a multi-select picklist. If records contain values that aren’t in the picklist definition, those values are deleted from those records when the data type changes.
D. Data is lost when changing Number to Currency - Changing to Currency from any other type can cause data loss
E. Data can be lost when changing from Rich Text to Long Text - You can convert rich text area fields into long text area fields only. Any images get deleted the next time you save the long text area field. After converting, markup is hidden in the long text area field but it isn’t removed from the record, so if you change your mind, you can restore the markup before you save the record.
https://help.salesforce.com/s/articleView?id=sf.notes_on_changing_custom_field_types.htm&type=5...

You can convert rich text area fields into long text area fields only. Any images get deleted the next time you save the long text area field.
https://help.salesforce.com/s/articleView?id=sf.notes_on_changing_custom_field_types.htm&type=5