full table scan or index scan

We are using database version 11.2.0.2

My developer is complaining that one query is running slow around 3 to 5 minutes.

SELECT * FROM T_TST_DATA WHERE  PRC_INFO_ID=’ C004’;

I looked at the database and found out that the table has three indexes. Only one index has the column name PRC_INFO_ID.

SQL> select column_name from dba_ind_columns where index_name='T_TST_DATA_INDEX1';

 

COLUMN_NAME

--------------------------------------------------------------------------------

PRC_INFO_ID

PRD_INFO_ID

TST_ID

TST_DATA_ID

So looks like his query is still using the full table scan. Thus, it is slow. My question is if the column does belong to a combination index, how can we make the query to use this index? Gurus, Please advise. Thanks.