At sixty, Maugham decided to withdraw from the theater and wrote The Summer Up, in which he tried to review what he _______ from his life and literature.

A．had learned

B．has learned

C．was learning

D．would learn

（6分）某科学家提出年轻热星体中核聚变的一种理论，其中的两个核反应方程为H＋C→N＋Q₁， H＋N→C＋X＋Q₂，方程中Q₁、Q₂表示释放的能量，相关的原子核质量见下表：

原子核	H	He	He	C	N	N
质量/u	1.007 8	3.016 0	4.002 6	12.000 0	13.005 7	15.000 1