骨的基本结构主要包括哪三个部分？（ ）
A：骨松质、骨密质和骨髓
B：骨膜、骨质和骨髓
C：骨松质、骨密质和骨膜
D：骨质、骨髓和骨髓腔
You can take anything from the shelf and read, but please ________ the books when you've finished with them.
