He published over 80 academic papers and contributed to numerous textbooks.
He has also contributed essays to textbooks about both ancient and modern China.
Secondary schools lack materials, from magazines to textbooks, to teach English.
He resigned in 1970 to devote more time to teaching and writing textbooks.
He is the author of over 140 papers and has contributed to several textbooks.
When it comes to textbooks - the really expensive books out there - the creative costs are enormous.
The first textbook appeared in 1775, though physicians had easy access to British textbooks.
"If there's an extra $3.5 million around, it should go to fixing schools and buying textbooks."
By the mid-1970s, however, he switched his writing efforts to textbooks.
It was first created in 1996, and is used extensively by teachers as an alternative to textbooks.