Definition: You will be given a context, a subject and a relation. Your task is to generate a question based on the subject and relation. The generated question should include the given subject. Try to use a minimum number of words that are not present in either context, subject or relation while generating question.

Positive Example 1 -
Input: Context : Isaac Nicola Romero (1916 in Havana, Cuba -- 1997) was a prominent Cuban guitarist and one of the founders of the modern Cuban Guitar School. 
Subject : Isaac Nicola 
Relation : place of birth
Output: What was Isaac Nicola's city of birth?

Positive Example 2 -
Input: Context : Both Timur and Demir are popular male names in Turkey today. 
Subject : Timur 
Relation : noble title
Output: What was the title that Timur held?

Negative Example 1 -
Input: Context : The Boeing 601 (sometimes referred to as the BSS-601, and previously as the HS-601) is a communications satellite bus introduced in 1987 by Hughes Space and Communications Company. 
Subject : Boeing 601 
Relation : service entry
Output: What is Boeing 601?

Negative Example 2 -
Input: Context : In 1956 and 1957, the British and Commonwealth system of battle honours recognised participation in the Battle of Villers-Bocage by the award to 11 units of the battle honour Villers Bocage, for service in expanding the bridgehead from 8--15 June. 
Subject : Battle of Villers-Bocage 
Relation : point in time
Output: who recognised participation in the Battle of Villers-Bocage?

Now complete the following example -
Input: Context : The Caledonian Railway 670 Class was a class of 0-4-2 steam locomotives designed by George Brittain for the Caledonian Railway (CR) and introduced in 1878. 
Subject : Caledonian Railway 670 Class 
Relation : service entry
Output: 


Output: Which was the official year for the approval of Caledonian Railway 670 Class?