题目

一种放射性元素的质量按每年10%衰减，这种放射性元素的半衰期(剩余质量为最初质量的一半所需的时间叫作半衰期)是(精确到0.1，已知lg 2＝0.301 0，lg 3＝0.477 1)( ) A．5.2                                        B．6.6 C．7.1                                        D．8.3His wife _____ his husband to give up smoking, but she failed. A. suggested B. persuaded  C. tried hard to persuade D. warned