Present perfect simple VS Present perfect continuous

Hello, all. I need your help.

- My hands are muddy because I __________ some flowers.

a. have planted
b. have been planting
c. bOth


"Aim High" (a book is published by Oxford university press, and the curriculum I teach) says that ONLY the present perfect continuous is possible. I wonder why we don't use the present perfect simple in such a context, i.e. there is an influence in the present (my hands are muddy). Furthermore, there's no indication that the action is in progress nor completed. Can we use BOTH?

Thanks in advance 🌹

Last edited by Hussein Hassan
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