第18题: [单项选择]The universe is estimated ___between 10 billion and 20 billion years old.
A. being B. to be C. which is D. is. 参考答案:B 答案解析:分析:estimate的用法比较单一;
1.be estimated to be/have/cost etc
The tree is estimated to be at least 700 ye
第19题: [多项选择]消化性溃疡患者疼痛的特点有() A. 周期性 B. 节律性 C. 昼重夜轻 D. 长期性 E. 持续性 参考答案:A, B, D