Correct Answer: curb

Solution : The first option is correct.

• Let's look at the meanings of the given word and the marked option:
  • Thwart : prevent someone from accomplishing something
  • Curb : restrain or keep in check
• Let's look at the meanings of the other given options:
  • Permit : give authorization or consent to someone to do something
  • Abet : encourage or assist someone to do something wrong, in particular, to commit a crime or other offence
  • Yield : produce or provide (a natural, agricultural, or industrial product)

Therefore, the correct answer is curb.