In today’s fast changing and petitive world, to be able to learn faster and more effectively is not merely desirable; it is .
A. essential
B. worthwhile
C. challenging
D. sufficient
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(答案→)A. essential
B. worthwhile
C. challenging
D. sufficient
解析： 句意：在今天的快速变化和有竞争力的世界，能够 学得更快更有效不仅是值得拥有的，也是基本的。四个选项的含义分别是：A. essential基本的，B. worthwhile值得的，C. challenging有挑战的，D. sufficient充分的，选A。