B-use of that is not correct.
D-change the meaning.
E- use of It is ambigous
Between A&C I will go for C as it is concise and gives clear meaning.

Why do you think a contrast is needed here?
Consider this example.
Because India has a prime minister who is Sikh, it doesn't bars a person of other religion to become the prime minister of India.
Does the above example requires contrast?
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Prepositional Phrases Clarified|Elimination of BEING| Absolute Phrases Clarified
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a)Because a manufacturer secures a patent for a pharmaceutical compound, the patent does not bar competitors from producing a chemical like it, as long as those chemicals have at least one structural difference with the patented compound ------ ‘from producing a chemical like it’ , ‘as long as those chemicals have’ see the shift in number. From a chemical, the choice incongruously shifts to ‘those chemicals’

b)That a manufacturer has secured a patent for one of its pharmaceutical compounds do not bar competitors from producing similar chemicals and having at least one important difference from the patented compound incorrect usage of having--- The subject of the sentence is the long --- That a manufacturer has secured a patent for one of its pharmaceutical compounds--- This is considered singular and hence the verb should be -- does not bar -- and not --do not bar--.

c) A patent for one of a manufacturer’s pharmaceutical compounds does not bar competitors from producing a chemical like the patented compound, as long as the two differ structurally in at least one way correct – Correct choice. You may see that this is a comparison between tow compounds and that one is the example of each other; use of ' such as' is wrong as you find in later choices. .

d)When securing a patent for one of a manufacturer’s pharmaceutical compounds, competitors are not barred from the production of chemicals such as the patented compound, provided that there is at least one structural difference --- 1. Modification problem 2. When we use a subordinate conjunction such as ‘when” it should be part of a full-fledged clause, with a noun verb and not with a simple participial phrase as comparing 3. 'such as' is wrong


e)Even if a manufacturer secures a patent for one of its pharmaceutical compounds, this does not bar competitors from the production of a chemical such as the patented compound, but having at least one structural difference from it. ----1. From the production is wrong idiom; from producing is the acceptable version 2. 2. 'Such as' are wrong 3. But having is a wrong structure. We cannot use a fanboy here to connect IC and a participial phrase 4. Do all the manufacturer’s put together produce one chemical? It should be chemicals rather


Nice question Kudo to Marcab
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Because A , B happens , as long as C occurs. This is the format of the given Question.
From seeing the options given . B , D , E gets eliminated Becoz of change in meaning.
Im stuck with A & C. I dunno wat s the answer.
I believe its time to give the correct OA atleast after a couple of weeks.

the answer is C ....

Choice A -> the patent does not bar competitors from producing a chemical like it, as long as those chemicals....

it" is ambiguous;
"difference with" is unidiomatic.
Agreement error between the 2 boldface.

Cheers