why not "make" instead of "made"?

[Chin]

English Grammar Tests, Elementary Level

ESL/EFL Test #92 "Using Make and Do (2)", question 8

He was confused and couldn't ......... up his mind about what to do next.

(a) make
(b) do
(c) made
(d) did

English Grammar Tests, Elementary Level

ESL/EFL Test #92 "Using Make and Do (2)", answer 8

He was confused and couldn't make up his mind about what to do next.

Correct answer: (a) make

Your answer was: incorrect
He was confused and couldn't made up his mind about what to do next.
_________________________

why not " make" instead?

that it comes after helping verb.

thank you veryyyy muh^^
Chin

[Yankee]

Hi Chin

The correct answer is indeed make.
Apparently you originally chose 'made' as the answer and 'made' is not correct.