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Am I aloud to pick Btec level 3 diploma in business in one block or do I have to choose them in both blocks
I presume that you mean in terms of subjects choice so If you are choosing the extended that is only one course. While there is another btec course that is equivalent to two alevels which is not sufficient to enter any uni with unless you've one or two alevels with it.
But you'll have to ask your educational establishment for further details