原级：backbone
1. Many of them have become experts in science management, professional backbones and business elites.
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2. Tourism, foreign trade and the service industry are the backbones of its economy.
3. They are the backbones of local economy and main contributors to both local GDP figures and revenues.
4. For thousands of years, children and land were the two backbones of rural elderly in China.
5. Roads that are not backbones of traffic should not be built too wide.