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Actually, I've never heard that rules. Usually, both present perfect simple and present perfect continuous are interchangeable. But there are some differences between them. In present perfect continuous

A1: "It has been raining for two hours"

A1 emphasises the continuity of the event(raining)

In the second example

A2: "It has rained for two hours

The continuity of the event is not important. BesideBesides, A2 takes "rained" as the current state.

Actually, I've never heard that rules. Usually, both present perfect simple and present perfect continuous are interchangeable. But there are some differences between them. In present perfect continuous

A1: "It has been raining for two hours"

A1 emphasises the continuity of the event(raining)

In the second example

A2: "It has rained for two hours

The continuity of the event is not important. Beside, A2 takes "rained" as the current state.

Actually, I've never heard that rules. Usually, both present perfect simple and present perfect continuous are interchangeable. But there are some differences between them. In present perfect continuous

A1: "It has been raining for two hours"

A1 emphasises the continuity of the event(raining)

In the second example

A2: "It has rained for two hours

The continuity of the event is not important. Besides, A2 takes "rained" as the current state.

1
source | link

Actually, I've never heard that rules. Usually, both present perfect simple and present perfect continuous are interchangeable. But there are some differences between them. In present perfect continuous

A1: "It has been raining for two hours"

A1 emphasises the continuity of the event(raining)

In the second example

A2: "It has rained for two hours

The continuity of the event is not important. Beside, A2 takes "rained" as the current state.