Difference between assess and assert

[doanngockhanh]

Test No. incompl/advan-27 "At the Doctors", question 7

Before she was allowed to leave the hospital, a physiotherapist had to ......... the extent of her mobility.

(a) assume
(b) accept
(c) assess
(d) assert

Test No. incompl/advan-27 "At the Doctors", answer 7

Before she was allowed to leave the hospital, a physiotherapist had to assess the extent of her mobility.

Correct answer: (c) assess

Your answer was: incorrect
Before she was allowed to leave the hospital, a physiotherapist had to assert the extent of her mobility.
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Dear Sir,
Why we use "assess" here instead of "assert"?
I don't quite understand the sentence. Please help me.
Thank you very much and Best regards

[Alan]

Assess means calculate/work out. Assert means say with conviction.
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