上消化道为()
A.从口腔到胃的一段消化管
B.从口腔到十二指肠的一段消化管
C.从口腔到空肠的一段消化管
D.从十二指肠
参考答案:B
The retired professor, _____ in his new book in the past three years, hasn’t realized the decline in his health.
A.involved
B.being involved
C.having involved
D.to be involved
受体