Why "alone" is the best alternative here?

[Javivaso]

Synonym Search, Intermediate level

ESL/EFL Test #114 "Synonyms for solitary and single", question 2

Marion went all ......... on this journey. All the others from the family decided to stay home.

(a) solitary
(b) lonely
(c) unaccompanied
(d) alone

Synonym Search, Intermediate level

ESL/EFL Test #114 "Synonyms for solitary and single", answer 2

Marion went all alone on this journey. All the others from the family decided to stay home.

Correct answer: (d) alone

Your answer was: incorrect
Marion went all solitary on this journey. All the others from the family decided to stay home.
_________________________

Why "alone" is the best alternative here?

thanks for the explanation
Javivaso

[Diverhank]

"All" and "alone" go together. In common usage, solitary is not usually used in this context. Coupled with "all" like "all solitary" sounds un-natural and funny...it's just not standard English...

[*Delta*]

i don't understand that one too???
why isn't alone the correct answer here???
can anyone help me understand that one please

[Yankee]