Why 'is' and not 'are'?

[Gzornenplat]

English Language Proficiency Tests, Advanced Level

ESL/EFL Test #621 "Real Life: The Internet and Websites (4)", question 4

E-......... involves buying and selling practices that is performed over the Internet.

(a) finance
(b) commerce
(c) money

English Language Proficiency Tests, Advanced Level

ESL/EFL Test #621 "Real Life: The Internet and Websites (4)", answer 4

E-commerce involves buying and selling practices that is performed over the Internet.

Correct answer: (b) commerce
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Why 'is' and not 'are'?

[Mister Micawber]

You're right. It should really be 'are'. We will fix this sentence. Thanks very much for letting us know.
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Native English teacher at Mister Micawber's