—Is it far from your home to your school? 

—Not very far. It is twenty minutes'walk, _______.[ ]

A. here and there

B. now and then

C. up and down

D. more or less

* * 毛滴虫不仅寄生于 * * ，还常侵入 * * 、 * * 旁腺甚至膀胱、肾盂。