Some more help with the following, please:
ACROSS:
4 Small thief accepting a lead album for cuttings(9): ?C?A?????
12 Unscrupulous member of the French Academy drops tenor(7):?M?????
DOWN:
18 Grant in the White House is novel ( 7 ): ?L?S?E?
21 Derived SI units from birds round the tracks ( 6 ): ?A?R??