Meaning of "by her delivery"

[Trillian]

English Language Proficiency Tests, Advanced Level

ESL/EFL Test #90 "High School Vocabulary", question 4

Although it's a complicated subject the professor managed to make it all totally clear and ......... by her delivery.

(a) lucid
(b) luminous
(c) lightening
(d) lifting

English Language Proficiency Tests, Advanced Level

ESL/EFL Test #90 "High School Vocabulary", answer 4

Although it's a complicated subject the professor managed to make it all totally clear and lucid by her delivery.

Correct answer: (a) lucid

Your answer was: correct
_________________________

Dear teacher,
could you explain the phrase "by her delivery".

Thank you,
Trillian

[Mister Micawber]

.
By her delivery = through or by means of her method of presentation.
.
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Native English teacher at Mister Micawber's