Which sentence is correctly punctuated?
a. she scribbled a quick reminder: "tues., jan. 1, is bob's birthday."
b. she scribbled a quick reminder: "tues., jan. 1 is bob's birthday."
c. she scribbled a quick reminder: "tues. jan. 1 is bob's birthday."
d. she scribbled a quick reminder: "tues, jan 1, is bob's birthday."

The best answer is A.

B is wrong because because, when a date follows a day of the week, standard usage is to set the date apart from the rest of the sentence using two commas (because the date functions as a separate clause). B uses only one comma.

C is wrong for the same reason, except that it uses no commas at all to set the date apart from the sentence.

D. is wrong because abbreviations require periods. Since "Jan" is meant to abbreviate "January," it requires a period after it; this sentence does not provide that period.