In this task, you're given a passage, further information available on a particular linked term from the statement, and a question. Your job is to generate the answer to the question by using the information provided. If there is no clear answer obtainable, output 'none'.

Let me give you an example: Passage: The group was occasionally diverted from strategic missions to carry out air support and interdiction missions. It supported Operation Overlord, the invasion of Normandy by attacking transportation targets, including bridges, along with airfields and strong points in France. On D Day, the squadron and the rest of the 446th Group led the first heavy bomber mission of the day. The 446th aided ground forces at Caen and Saint-Lo during July by hitting bridges, gun batteries, and enemy troops. During Operation Market Garden, the attempt to seize a bridgehead across the Rhine in the Netherlands, the 704th dropped supplies to allied troops near Nijmegen. It struck lines of communications during the Battle of the Bulge. During Operation Varsity in March 1945, it supplied ground and airborne troops near Wesel. The squadron flew its last combat mission on 25 April 1945 against Salzburg, Austria. The group had flown 273 missions and had lost 58 aircraft during the war,
. Link Information: Operation Market Garden was a failed World War II military operation fought in the Netherlands from 17 to 25 September 1944. Question: When did the operation during which the 704th dropped supplies to allied troops near Nijmegen begin?
The answer to this example can be: from 17 to 25 September 1944
Here is why: The passage describes the 704th's actions during Operation Market Garden, and the answer specifies when the operation happened.

OK. solve this:
Passage: The first archaeological investigation of the site was carried out in 1964. In that year, the site was noted during an archaeological survey of the region directed by Maurits N. van Loon of the Oriental Institute of the University of Chicago, and a small sounding was made. In 1965, a more extensive excavation was carried out, again under the direction of Van Loon. Between 1971 and 1974, work on the site was resumed by a team of the French Centre national de la recherche scientifique (CNRS) directed by Jacques Cauvin. All excavations were part of the larger international and eventually UNESCO-coordinated effort to investigate as many archaeological sites as possible in the area that would be flooded by Lake Assad, the reservoir of the Tabqa Dam, which was being built at that time. The filling of Lake Assad eventually led to the flooding of Mureybet in 1976. Although the site is now submerged and no longer accessible, the material that has been retrieved during the excavations continues to generate new research. This material is currently stored at the National Museum of Aleppo and the Institute de Prehistoire Orientale in Jales-Berrias in France.
Link Information: The dam was constructed between 1968 and 1973 Question: When did the construction of the dam that flooded Mureybet begin?
Answer:
Answer: 1968