Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_78601 ( "Year" real, "Competition" text, "Venue" text, "Position" text, "Event" text, "Time" real )

### Question ###
What is the greatest Time with a Year of 1991, and Event of 4x100 m relay?

### Accurate SQL ###

SELECT MAX("Time") FROM table_78601 WHERE "Year" = '1991' AND "Event" = '4x100 m relay'