a. 不能解决的

[经] 不能偿还的(债务), 不兑现的(纸币)

[ adj ]
not easily solved
<adj.all>
an apparantly insolvable problempublic finance...had long presented problems unsolvable or at least unsolved

Insolvable \In*solv"a*ble\, a.
1. Not solvable; insoluble; admitting no solution or
explanation; as, an insolvable problem or difficulty. --I.
Watts.

2. Incapable of being paid or discharged, as debts.

3. Not capable of being loosed or disentangled; inextricable.
``Bands insolvable.'' --Pope.