Choose
I've studied / been studying Arabic for three years, but I still struggle with some aspects of the grammar.
been studying
When I met him, he had already acquired / had already been acquiring a second language.
had already acquired
I've been knowing her for ten years.
I've known her for ten years.
She started learning Arabic three years ago and she is still learning it.
(BEEN)
She ___________________ Arabic for three years.
She has been learning Arabic for three years.
By the time she moved to Spain, she had acquired / had been acquiring a good level of competence in Spanish.
had acquired
I've not put / not been putting my Arabic into practice recently, so it's getting rusty.
haven't been putting
When I arrived, they have already started the presentation.
When I arrived, they had already started the presentation.
He started studying German five years ago and she still studies it.
(STUDYING)
She _________________ for five years
She has been studying German for five years
He's exhausted because he has worked / has been working on his pronunciation all morning.
has been working
By the end of the course, students will have acquired / will have been acquiring the vocabulary they need to hold a conversation.
will have acquired
I've been getting accustomed to the new system since three months.
I've been getting accustomed to the new system for three months.
He finally understood the complex grammatical concept.
(GRASPED)
She finally grasped the complex grammatical concept.
By next June, I will have attained / will have been attaining a C1 level of competence.
will have attained
She was frustrated because she had struggled / had been struggling with listening comprehension for months.
had been struggling
By next year, I will study English for six years.
By next year, I will have been studying English for six years.
He started using English at work six months ago, and it now feels normal to him.
(ACCUSTOMED)
He has become accustomed to using English at work.
She has barely grasped / has barely been grasping the basic concepts, so she's finding the advanced material difficult.
has barely grasped
English pronunciation has undergone / has been undergoing a steady shift over time.
both can work depending on whether you emphasise the completed change or the ongoing process.
She has been grasping the concept, so she can explain it now.
She has grasped the concept, so she can explain it now.
By the end of this academic year, she will have completed ten years of English study.
(BEEN)
By the end of this academic year, she will have been studying English for ten years.