The company failed to pay up the loan because it had become …

Step 1: Analyze the question The sentence says the company failed to pay up the loan and gives a reason: "because it had become ......". We need the word that explains an inability to pay a debt.

Step 2: Explain the concept This tests vocabulary in context. The key is the cause-and-effect link: failing to repay a loan points to a financial condition, not just a character or performance flaw.

Step 3: Check each option

• A. corrupt means dishonest or immoral, especially in handling power or money. It describes behavior, not inability to pay.
• B. bankrupt means legally declared unable to pay debts, or having no money left. This fits the sentence directly.
• C. inefficient means not working in a well-organized way. It's a weak, indirect reason for not paying a loan.
• D. unreliable means not dependable. It describes a trait, not a cause for being unable to pay.

Step 4: Answer "The company failed to pay up the loan because it had become bankrupt.

Tip: In "best completes the sentence" questions, look for the word that gives a direct reason for the result. Words like loan, debt, and failed to pay are strong clues for bankrupt. Also remember the spelling: bank-rupt (from Latin rupt, "broken").