钱学森《现代自然科学中的基础学科》一文的文体是（）
A.说明文
B.记叙文
C.科学论文
参考答案：A
Mary devoted all her money she owned ___________ people in need.
A to help B helping C helped D to helping
—Where is Li Lei? Do you know?
—He's _____ the apple tree.[ ]
A. in
B. on
C. at
D. down
