题目

Alex Palmer Haley (1925―1992) became famous for the publication of the novel Roots, which traces (追踪) his ancestry (祖先) back to Africa.Alex Haley was born in Ithaca, New York. His father was a teacher of agriculture and his mother was a music teacher. The family moved to the small town of Henning, Tennessee, when Haley was very young.Haley did not do very well at school or university. During World War II, Haley enlisted (参军) in the Coast Guard. He started to write adventure stories to keep off the boredom, and thus became Chief Journalist. After 20 years of service, Haley left th 若函数f(x)是R上的单调递增函数，则实数a的取值范围为 [　　] A． (1，＋∞) B． (1，8) C． (4，8) D． [4，8)