But if there's a result in the present, we tend to use the present perfect. I've lost my phone. Can you call me? (present perfect) I lost my phone last week, but someone handed it in. (past simple) 2.

Catalytic hydrogenations are key processes in the fine chemical and pharmaceutical industries, but the development of such processes is challenging due to aspects such as catalyst deactivation, metal ...

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Free worksheet ... simple, continuous, perfect, and perfect continuous. Technically, there are only two grammatical tenses in English: present and ...

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