English question, please help?

(1) " Electric vehicles have traditionally lost more of their value than petrol vehicles." ----- (✓)
i) " Electric vehicles have .... lost .... their value "
　"Electric vehicles" 是眾數, ∴ use "their"

ii) Q: Why is there no "s" to make value plural in the sentence?
　"value"=價值 can be "countable" or "uncountable".
　This sentence refers to the value of "electric vehicles"
　"value" here is taken as one WHOLE thing --- 電動車的「整體價值」, ∴ no "s" to make value plural！

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(2) " China has undergone a great many changes over the last few years." ----- (✓)
China has undergone a great change . . . [ 中國巳經歷過一項重大的轉變 . . . ]
China has undergone many changes . . . [ 中國巳經歷過很多的轉變 . . . ]
China has undergone a great many changes . . . [ 中國巳經歷過非常多的轉變 . . . ]

Note :-
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i) a change ≡ 一項轉變 , many changes ≡ 多項/很多 轉變, a great many changes ≡ 非常多/很多很多 的轉變
ii) "a great many" is a phrase, meaning "many many".
　"a great many" is of the same form as "a lot of". Each of these is a unique phrase.
　That is, we don't have phrases such as "great many" or "lot of"！
iii) Since "a great many" refers to 眾數, ∴ followed by a 眾數 noun --- "changes".