Consider the following sentence:
- Have you been watering the plants?
Is the above sentence grammatically correct? Or should it be something like:
- Have you been watering the plants for 5 minutes?
i.e. when you see the use of 'have been' with present participle form you also use the time of start.
Best Answer
You can certainly use the present perfect continuous without an expression of time. In such a case you are interested only in the activity, not in its starting point or duration. For example:
If you want to emphasise when you started the activity, you need to use since:
And if you want to emphasise the duration, you need to use for:
The specific question Have you been watering the plants for 5 minutes? is grammatical but unlikely. One possible scenario is that your wife has asked you to water the plants for 3 minutes only and suspects you might have exceeded the time limit she set.