'Abandon' is a verb which means 'to desert, to dump or to cast aside'. Option D - 'Forsake' is a verb which means 'to desert, to abandon or to disown', which is similar to the meaning of the given word.
On the other hand, Option A - 'Admit' is a verb which means 'to acknowledge, to confess, or to recognize', Option B - 'Retain' is a verb which means 'to keep, to maintain or to continue', Option C - 'Claim' is a verb which means 'to assert, to affirm or to declare', none of these options give same meanings as of the given word 'Abandon'.
Therefore, the most appropriate synonym for 'Abandon' is Option D - Forsake.