In this question,
"Tell" (plural form) does not modify 'substances', rather it modifies 'one of the substances' (singular).
The point to be noted here is that how can the plural verb 'Tell' modify singular subject 'One of the substances'.
As the sentence has 'BELIEVE' in it, the verb can only take the base form. So irrespective of the subject being singular/plural, the verb will always take the base form.
Hence the correct answer is 'A'.
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...
"Tell" (plural form) does not modify 'substances', rather it modifies 'one of the substances' (singular).
The point to be noted here is that how can the plural verb 'Tell' modify singular subject 'One of the substances'.
As the sentence has 'BELIEVE' in it, the verb can only take the base form. So irrespective of the subject being singular/plural, the verb will always take the base form.
Hence the correct answer is 'A'.
Posted from my mobile device
...
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