Which of the following taxpayers is required to file a tax return?

Question $4$ options:

a$.$ Howard and Ellen, who are newly married at age $25$ and $26$ respectfully. Ellen earns $$25,000$ from her job while Howard doesn't work because he is disabled.

b$.$ Dan, age $12,$ who earned $$200$ from running a lemonade stand and will be claimed by his parents on their tax return.

c$.$ Sally, age $55,$ who earned $$1500$ as self$-$employed author and cannot be claimed as a dependent of anyone.

d$.$ Eleanor, age $75,$ who receives $$13,000$ from a pension and cannot be claimed as a dependent of anyone.