The founder of quantum mechanics (量子力学) and the inventor of the uncertainty principle, Werner Heisenberg was born in Wurzburg and brought up in Munich, where he entered the university in 1920 to study physics under Arnold Sommerfeld. After a brief stay at Gottingen University, he moved to Copenhagen to pursue research under Niels Boho and remained there until 1927.
After 1913 the quantum theory made considerable progress, but by 1924 it was running out of steam, largely owing to its lack of a coherent and systematic mathematical foundation. In the summer of 1925 Heisenberg discovered the foundation of just such a mechanics. Then his theory was rapidly developed by Max Born, Pascual Jordan, and P. A.M. Dirac.
In the spring of 1927, while a lecture at Boho's institute, Heisenberg followed up his discovery of the uncertainty relations, which are of central importance in quantum mechanics.
Heisenberg was awarded the Nobel Prize for Physics in 1932 for his contribution t9 the development of quantum mechanics. From 1927 to 1941 he was professor of theoretical physics at the University of Leipzig. Although privately unsympathetic to the Nazi regime he remained in Germany throughout the Second World Wax, seeing it as his duty to work for the preservation of German physics and its future reconstruction. From 1941 to 1945 he was Director of the Kiser Wihelm Institute for Physics at Berlin, where he worked with Otto Hahn on the development of a nuclear reactor. After the war he became Director of the Max Planck Institute for Physics and played a prominent part in the promotion of scientific research in Germany.
Heisenberg has an important part in 20th century thought: the notion of uncertainty which he introduced is, like Einstein's concept of relativity, one of the major idea of the century; it has changed not only physics but our entire world picture.
When was the firm foundation of quantum theory laid？

A. In 1913.
B. In 1924.
C. In 1925.
D. In 1927.