题目

Experience the newly opened Grand Canyon(大峡谷) West Skywalk in Colorado. Departing from Grand Canyon South Rim by Airplane to Grand Canyon's West Rim, you will land and take a ground tour to the Skywalk! Walk on air for 70' feet over the edge of Grand Canyon West. This Skywalk has been open since March 28, 2007. Daily visitorship to the Skywalk has been over 4,000 people. Please be patient to enjoy your moment on the Skywalk. After you have experienced the one and only Grand Canyon Skywalk Glass Bridge, you will return to the Grand Canyon West Airport and take your Airplane for a flight b取一只小鼠的皮肤，分别移植到切除和不切除胸腺的幼年小鼠身上，切除胸腺小鼠的皮肤移植更易成功。这个实验结果说明对异体皮肤排斥起重要作用的是 （  ）A．造血干细胞B．T细胞C．B细胞D．吞噬细胞