参考答案：B

解析：

The key word is "unreliable. " The completed contract method is used when cost estimates are unreliable. The percentage-of-completion method recognizes profit corresponding to the percentage of cost incurred to total estimated costs associated with long-term construction contracts. Percent-of-completion is used where contracts and cost estimates are reliable. The installment sales method recognizes revenue and associated cost of goods sold only when cash is received. Gross profit (sales-cost of goods sold) reflects the proportion of cash received. The cost recovery method is similar to the installment sales method but is more conservative. Sales are recognized when cash is received, but no gross profit is recognized until all of the cost of goods sold is collected.