Correct Answer: A

Rationale: The correct answer is A: 0.09%. To convert 0.0009 to a percentage, move the decimal point four places to the right and add a percentage sign. Therefore, 0.0009 is equal to 0.09%. Choice B (9%) is incorrect as it represents 0.09 without the decimal point adjustment. Choice C (0.01%) is incorrect as it represents 0.0009 with one less zero. Choice D (0.90%) is incorrect as it represents 0.9 not 0.0009.

Correct Answer: B

Rationale: To find the number of people who could swim, multiply the total number surveyed by the percentage who said they could swim. In this case, 85% of 120 people is calculated as 0.85 * 120, resulting in 102 people who could swim. Choice A (100) is incorrect because this does not account for the percentage that said they could swim. Choice C (110) is incorrect as it is above the total number surveyed. Choice D (90) is incorrect as it does not consider the percentage who said they could swim.

Correct Answer: C

Rationale: Reducing the rat's speed by 50% means it will take twice as long to finish the maze. Since the original time is 3 minutes, doubling that gives 6 minutes. Therefore, the total time will be 6 minutes, making the correct answer C. Choice A (3 minutes) is the original time it takes the rat to finish the maze, not the time with the backpack. Choice B (4 minutes) is not correct as reducing the speed by 50% would double the original time. Choice D (1.5 minutes) is incorrect as halving the time is not the effect of reducing the speed by 50%.

Correct Answer: C

Rationale: To find the perimeter of a shape with equal sides, you multiply the length of one side by the number of sides. In this case, the honeycomb cell has 6 sides, each measuring 8mm. Therefore, the perimeter is calculated as perimeter = number of sides * side length = 6 * 8mm = 48mm. Choices A, B, and D are incorrect because they do not correctly calculate the total length around the honeycomb cell with six sides.

Correct Answer: C

Rationale: To find the percentage of 8 in 40, divide 8 by 40 to get 0.2. Multiply this result by 100 to convert it to a percentage: 0.2 100 = 10%. Therefore, 8 is 10% of 40, making choice C the correct answer. Choices A, B, and D are incorrect percentages calculated from incorrect divisions and multiplications.