Finding Variable IDs

Looking to create tables in R using VariableIDs, I have no problem finding the variables for the year 2019, however, the variable IDs for the previous years (2018, 2017,...,2009) are different. Does anyone knows how to find those variable IDs??

Examples:

Total_OppositeSex_Marriage_19 <- get_acs(geography = "US",
                                           variable = "B09019_010",
                                          survey = "acs1",
                                          year = 2019)

Total_OppositeSex_Marriage_18 <- get_acs(geography = "US",
                                           variable = ""???",
                                          survey = "acs1",
                                          year = 2018)

Thank you!!