9Where it is material for any purpose which of two or more possible assets are taken to constitute exempt property—
(a)such assets shall be taken to fall within paragraph (c) of subsection (1) of the principal section as are most favourable to the widow or widower, and any agreement between the widow or the widower and the Commissioners as to what assets will be most favourable shall be conclusive ;
(b)subject to sub-paragraph (a) above, property bearing its own duty shall be taken to be exempt property before property not bearing its own duty ; and
(c)subject to sub-paragraphs (a) and (b) above, each of the assets shall be so taken to the extent proportionate to its value.