Generate a correct and concise answer for the question based on the words in the context.
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Question: Context : The Type 97 motorcycle, or Rikuo, was a copy of a Harley-Davidson motorcycle produced from 1935 in Japan under license from Harley-Davidson by the Sankyo Company (later Rikuo Nainen Company). 
Question : What was the year Type 97 motorcycle entered service?

Answer: 1935


Question: Context : The Sinclair Scientific calculator was a 12-function, pocket-sized scientific calculator introduced in 1974, dramatically undercutting in price other calculators available at the time. 
Question : What was the year Sinclair Scientific entered service?

Answer: 1974


Question: Context : South African Airways Flight 228 was a scheduled flight of the Boeing 707-300C Pretoria, registration ZS-EUW, on 20 April 1968 from Johannesburg to Heathrow via Windhoek, Luanda, Las Palmas and Frankfurt. 
Question : What is the full date that South African Airways Flight 228 crashed on?

Answer:
20 April 1968