The correct answer is: D. 1920.
The Dacca Students Union was established in 1920. It was founded by a group of students from the University of Dhaka, including A.K. Fazlul Huq, Huseyn Shaheed Suhrawardy, and Kazi Nazrul Islam. The union played a major role in the Bengali Language Movement of 1952 and the Bangladesh Liberation War of 1971.
Option A: 1885 is incorrect because the Dacca Students Union was not established until 1920.
Option B: 1890 is incorrect because the Dacca Students Union was not established until 1920.
Option C: 1910 is incorrect because the Dacca Students Union was not established until 1920.
Option D: 1920 is correct because the Dacca Students Union was established in 1920.