I have a question regarding this explanation. Can I use present perfect in A and present perfect continuous in B? Will past simple work in B?
"For the context of changing to a new course, we say A: "I've been studying English for the last two years, but now I'm switching to a new course" at any point after you made the decision to change courses but before your last day on the English course. Once your last day is finished, you'd say B:"I've studied English for the last two years but tomorrow I start my French course".