Why is 'execute' not appropriate?

[Asterix]

Synonyms Lesson, Advanced Level

ESL/EFL Test #114 "Synonyms for kill and murder", question 5

The mafia people usually kidnap rich men's children for money and after that they ......... them.

(a) assassinate
(b) execute
(c) murder
(d) destroy

Synonyms Lesson, Advanced Level

ESL/EFL Test #114 "Synonyms for kill and murder", answer 5

The mafia people usually kidnap rich men's children for money and after that they murder them.

Correct answer: (c) murder

Your answer was: incorrect
The mafia people usually kidnap rich men's children for money and after that they execute them.
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Why is 'execute' not appropriate?

Asterix

[lost_soul]

execute is what the Government does to its convicted to death criminals.
the mafia is a bunch of criminals who only kill or murder innocent people (or assassinate politicians who are part of the Goverment)
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Alex

"Noone has ever escaped from Stalag 13"
Colonel Klink, Kommandant of Stalag 13

[Yankee]

The word 'murder' is the best choice, but I wouldn't say that 'execute' is completely wrong in this sentence. In this sort of context, however, we'd usually say something such as "murdered/killed execution-style" (rather than "executed") if a murder is carried out in a way that resembles an execution:
http://en.wikipedia.org/wiki/Execution-style_murder

@Torsten
I think quite a few of the sentences in this test could use some fine-tuning.
In this particular question, for example, the phrase "the mafia people" is quite unnatural. The word 'Mafia' is generally capitalized, and a member of the Mafia is called a "mafioso" (plural = "mafiosi").
.
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Amy
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ESL teacher, translator, and a native speaker of American English

[Torsten]

Hi Amy,

Thanks a lot for your suggestions -- we'll make the changes asap.
Regards,
Torsten
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Test Of English for International Communication
TOEIC Preparation & TOEIC Vocabulary