Spelling exercises: "er" vs "re"

Some words that are pronounced /ər/ are spelled with "re" in British English and with "er" in American English. Other words are spelled with "er" under both conventions.

/ər/

 * The following words are always spelled with "re" in British English and with "er" in American English.
 * centre - fibre - litre - metre (unit of length) - sepulchre - spectre (ghost) - theatre


 * Always "re"
 * acre - hors d'ouvre - mediocre - ogre - Spectre (James Bond film)


 * Always "er"
 * after - alter - brother - consider - daughter - differ - ever - father - meter (device) - never - number - offer - order - other - over - soccer - under - voter - water

/ɜː/

 * deter - prefer - refer - transfer