A: True. This statement will work if customer_id is a character data type in the database. Oracle will implicitly convert the numeric literal 0001 to a string to compare with customer_id.
D; True. If the insert_date is of type DATE and the NLS_DATE_FORMAT matches 'DD-MON-YY', Oracle will implicitly convert the string literal '01-JAN-19' to a date type to compare with insert_date.
B:is incorrect because if customer_id is a numeric data type, there is no need for implicit conversion. C is incorrect because using the DATE literal DATE '2019-01-01' is an explicit conversion. E is incorrect because TO_CHAR(customer_id) is an explicit conversion from a numeric to a string data type.