39405
The existence of the Colossus machines was kept secret until the mid-1970 s ; the machines and the plans for building them had previously been destroyed in the 1960 s as part of the effort to maintain the secrecy of the project .
 None
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: location, person, organization 
Text: {0} 
 Entities:  
Answer:
 None