JAMB - English Language (1979 - No. 18)
Mr. Thomas talked .... about the successes of his institute in the past year.
at a great length
for great length
at great length
for a great length
at great lengths
Spiegazione
The phrase "at great length" is an idiomatic expression that means in great detail or for a long time. The article 'a' or the plural 's' should not be attached.