柴油机的速度特性指()随转速变化的规律。
参考答案:有效功率、有效转矩、有效燃油消耗率
Tina, ________ for months to find a job as a waitress, finally worked as a tour guide at a local advertising agency.
A.struggling
B.struggled
C.having struggled
D.to struggle
地球上最大的生态系统叫做 ( )
A.生物圈
B.大气圈
C.水圈
D.岩石圈