A reliable shortcut for relative-clause agreement errors is to isolate the relative pronoun, trace it back to its antecedent noun, and then mentally replace "who" with that noun to test the verb directly.
In phrase (b), "and with others who also uses the win-win approach", the relative pronoun "who" stands in for "others". Replacing "who" with its antecedent gives: "others also uses the win-win approach". Read this way, the error becomes immediately obvious: "others" is plural, but "uses" is the singular present-tense form (the kind that takes an -s ending, like "he uses" or "she uses"). A plural subject like "others" needs the plain form "use", exactly as "assertion is used" in phrase (a) correctly pairs a singular subject with a singular verb form.
Checking the remaining phrases the same way: "each party can consider" (c) pairs a singular subject with a modal verb that does not change with number, so no issue arises; "a solution that satisfies" (d) correctly uses the -s form because "solution" is singular. Only phrase (b) breaks the pattern.
The correct answer is option 2, phrase (b).
Identify the part of the sentence that contains an error:
"Neither the manager nor the employees ___ willing to accept the new policy."