Historical clue formulations

• Kind of acid found in asparagus — 2020-06-14
• ___ acid — 2018-06-23
• ___ acid (vitamin B9) — 2015-03-15
• Kind of acid in breakfast cereal — 2012-01-17
• Kind of acid found in spinach — 2010-08-08
• ___ acid (B vitamin) — 2004-06-28
• Kind of acid — 1996-05-23