I think my 3 D answer works - and 1 A didn't change it.
3 D. Stone bridges are to weaken (5)
The S is superfluous, so Tone....
Tone gives Tint and 'a'/are went inside (bridges), so Taint, weaken.
That fitted in with the T in 1 A.
My parsing isn't always great, but everything fitted in OK!