Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Month | 15th- 20th century | U.S. (1912) | U.S. (2013) | Britain (2013) | Hindu |
| --- | --- | --- | --- | --- | --- |
| January | garnet | garnet | garnet | garnet | serpent stone |
| February | amethyst , hyacinth , pearl | amethyst | amethyst | amethyst | chandrakanta |
| March | heliotrope , jasper | heliotrope , aquamarine | aquamarine , heliotrope | aquamarine , heliotrope | Gold Siva-linga |
| April | diamond , sapphire | diamond | diamond | diamond , rock crystal | diamond |
| May | emerald , agate | emerald | emerald | emerald , chrysoprase | emerald |
| June | cat's eye , turquoise , agate | pearl , moonstone | pearl , moonstone , alexandrite | pearl , moonstone | pearl |
| July | turquoise , onyx | ruby | ruby | ruby , carnelian | sapphire |
| August | sardonyx , carnelian , moonstone , topaz | sardonyx , peridot | peridot | peridot , sardonyx | ruby |
| September | chrysolite | sapphire | sapphire | sapphire , lapis lazuli | zircon |
| October | opal , aquamarine | opal , tourmaline | opal , tourmaline | opal | coral |
| November | topaz , pearl | topaz | topaz , citrine | topaz , citrine | cat's-eye |
| December | heliotrope , ruby | turquoise , lapis lazuli | turquoise , zircon , tanzanite | tanzanite , turquoise | topaz |
Question:
What was the U.S birthstone in the 15th-20th century when in 2013 it was amethyst?
Answer:
amethyst , hyacinth , pearl