A common problem in the UK! Not sure who (or if) you are accredited with but certainly the ITSSAR syllabus says that c ones aren't suitable because of the gaps between etc...
Having faced this problem for over 30 years now (god that makes me feel old) I've done various things, mainly laying concrete blocks across the base of the pallet or wedging another pallet against it to hold it up. Not ideal but needs must sometimes!
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