Why we can't use "thankfulness" or "gratefulness" here?

[Angel]

Hi Alan & Torsten

I discovered your web-site yesterday. It is excellent.I wanna congratulate you first( thanks for being free) then I wanna ask a question.

Test No. incompl/advan-4 "Newspaper Headlines", question 7
In her speech she expressed her ......... for all the help she had been given.

(a) thankfulness
(b) gratitude
(c) gratefulness
(d) thanking

Test No. incompl/advan-4 "Newspaper Headlines", answer 7

In her speech she expressed her gratitude for all the help she had been given.

Correct answer: (b) gratitude

In her speech she expressed her gratitude for all the help she had been given.
In the answers we both have thankfulness and gratefulness so I can find the correct answer but If there was only one of them I couldn't find it. In short can you explain why we can't use thankfulness or gratefulness here.Thank you in advance.

[Alan]

Hi Angel,

Thanks for your comments about the site. Gratitude means thanks and to express gratitude simply means to say thank you. Thankfulness means relief that something has or has not happened. In other words if you are grateful, you are pleased and say thanks. If you are thankful you are pleased and say you are relieved - in the sense of breathing a sigh of relief. Gratefulness exists as a word but is rarely used and then only to describe someone's pleasure in everything in life - a rather poetic concept.

Alan
_________________
English as a Second Language
You can read my ESL story Saying It Twice

[Angel]

Hi Alan,
Now it is clear, thank you

[Thameem]

Hi Alan, can you explain to me the difference between thankfulness, greatfulness, gratitude. I can't understand why gratitude here instead Greatfulness, I am trying to understand the first explanation but still do not understand, your explanation highly appreciated.