Which four statements correctly describe functions that are available in SQL? （）
- AINSTR returns the numeric position of a named character.
- BNVL2 returns the first non-null expression in the expression list.
- CTRUNCATE rounds the column, expression, or value to n decimal places.
- DDECODE translates an expression after comparing it to each search value.
- ETRIM trims the heading or trailing characters (or both) from a character string.
- FNVL compares two expressions and returns null if they are equal, or the first expression if they are not equal.
- GNULLIF compares two expressions and returns null if they are equal, or the first expression if they are not equal.