delta|deltas

希腊字母表的第四个字母是delta。

The fourth letter of the Greek alphabet is ___delta.

医生比较了患者治疗前后的血压变化。

The doctor compared the ___deltas in blood pressure before and after treatment.

长江三角洲是中国最肥沃的农业区之一。

The Yangtze River ___delta is one of China's most fertile agricultural areas.