Assure vs. assert

[Curzio Malatesta]

English Language Proficiency Tests, Advanced Level

ESL/EFL Test #30 "Letter Writing (2)", question 6

I can ......... you that the duties are not in any way complicated.

(a) confirm
(b) assure
(c) assert
(d) affirm

English Language Proficiency Tests, Advanced Level

ESL/EFL Test #30 "Letter Writing (2)", answer 6

I can assure you that the duties are not in any way complicated.

Correct answer: (b) assure

Your answer was: incorrect
I can assert you that the duties are not in any way complicated.
_________________________

Hello Alan,
Why 'assure' and not 'assert'? The writer knows that the 'best man' job is not complicated without any doubt.

Curzio Malatesta