Phrase: completely lost track of what he was saying

English Language Tests, Intermediate level

ESL/EFL Test #61 [color=blue]“Losing It (1)”, question 7

I followed as much as I could of his arguments but then I gave up because I’d completely lost of what he was saying.

(a) pace
(b) route
(c) path
(d) track

English Language Tests, Intermediate level

ESL/EFL Test #61 [color=blue]“Losing It (1)”, answer 7

I followed as much as I could of his arguments but then I gave up because I’d completely lost track of what he was saying.

Correct answer: (d) track
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Dear Teachers

I don’t know what word is right here. Can you help me and explain that phrase for me, please?

Thank you
Thu

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The idiom required is ‘lose track’ (= no longer be informed or know about something or someone). The other words do not make idioms here and are meaningless in this sentence.
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