a) The road that / which connects the two villages is very narrow.
b) George showed me some pictures that / which had been painted by his father.
Can a) be considered a non-defining or defining relative clause? Or both?
NOT A TEACHER
(1) Here in the States, many teachers tell us learners to use only."that" for defining/
restrictive clauses. (I hear that in other Englishes, the "rule" is not so strict.)
(2) IMHO, both of your sentences are restrictive, so maybe you should consider
(3) As you already know, you could change "a" to non-restrictive by adding some commas.
The road, which connects the two villages, is very narrow.