Original sentence: After receiving his BS degree from the University of Southern California in 1918, he served in the US Army and then worked at the Los Angeles Bureau of Power and Light.In 1926, he obtained his MS from the University of Southern California.In 1928 he received his PhD (under Paul Sophus Epstein) from Caltech
Edited sentence: After receiving a BS degree from the University of Southern California in 1918, he served in the US Army and then worked at the Los Angeles Bureau of Power and Light.In 1926, he obtained an MS from the University of Southern California.In 1928 he received a PhD (under Paul Sophus Epstein) from Caltech