3a is one of the "12" - think of the "longlife" battery advertised on tv with the bunny, then take "race" out of it.
Your ebtry for 3a will then be the other word associated with your answer to the clue.
13a again it's one of the 12
19a think of a word for height then take out the R - gives you ?????? and the sphinx at Giza is an example of one.