Dr. Nien was famously reluctant to have his biography written. But \_\_\_\_ Nien since 1990, Mr. Feng, the author of a critical study of Dr. Nien's work, received not only his friend's permission but access to a large collection of his manuscripts.
Ahave known
Bhaving known正確答案
Cknew
Dto know
答案與詳解
