Question

The author mentions Professor Hodous's 16 years of missionary service in China primarily to

demonstrate that Professor Hodous is committed to treating Buddhism fairly
indicate why Professor Hodous should be considered an expert on Buddhism
point out that Professor Hodous has a religious bias regarding Buddhism
show that Professor Hodous is a deeply religious person

Answer 1

The author mention Professor Hodous' sixteen years of missionary service in China primarily to DEMONSTRATE THAT PROFESSOR HODOUS SHOULD BE CONSIDERED AN EXPERT ON BUDDHISM.
The author mentioned the years of experience of the professor in order to show that the professor has solid background in Buddhism and know all that is there to be known about the religion, that is, he is an expert when it comes to that religion.

Answer 2

The correct answer is "committed to treating Buddhism fairly". Professor Hodous wrote this volume on Buddhism in China, one of the important centers of Buddhism. He has taken pains to exhibit and to interpret the religious life of the peasant as affected by Buddhism. He was absolutely fair to Buddhism, but still to express his own conviction that the best that is in Buddhism is given far more adequate expression in Christianity.