4. Had the patient followed the doctor's advice, he would have recovered long ago.(过去时）

(=If the patient had followed the doctor's advice …）

要是病人当初能听从医生的劝告，他早就恢复健康了。

5. The patient must be instructed that, should his condition not improve within 48 hours, or deteriorate within this time, he should seek medical advice without further delay.(将来时)

(=The patient must be instructed that, if his condition should not improve...)

必须嘱咐病人，万一病情在48小时内未见改善或有所恶化，应立即就就医。6. The heart would very soon fail if the stream of blood which furnishes its muscle with oxygen and nourishment, should dry up. （将来时）

如果给心肌提供氧气和养料的血液干涸，心脏很快就会衰竭。

虚拟条件句还可用 if it were not for(现在时）或if it had not been for(过去时)这种句型来表示，意为“要不是”“若没有”（相当于短语介词but for)。其中连词if可以省略,但必须使用倒装结构，即were it not for 或had it not been for,将来时虚拟条件句的谓语也可用were to十动词原形。 举例如下：

7. If it were not for the science of blood transfusion, many thousand people would have had little chance of recovery. (现在时）

如果没有输血这门科学，成千上万的人就很少有康复的机会。

8. The patient would have died of gastric cancer had it not been for the timely operation.(过去时）

(=…if it had not been for ...)

要不是及时手术，患者就会死于胃癌。

9. Were it not for the modern equipment, such operations would not be performed. (现在时）

(= If it were not for the modern equipment,…）

要是没有这种现代化设备，这些手术就无法进行。