我国南海海底蕴藏固体“可燃冰”。可燃冰的主要含成分是甲烷水合物（由甲烷和水组成），甲烷水合物的化学式为CH4·8H2O。关于“甲烷水合物”的叙述不正确的是
A．甲烷水合物由碳、氢、氧三种元素组成
B．甲烷水合物充分燃烧后的产物是二氧化碳和水
C．CH4·8H2O中甲烷和水的质量比为1:8
D．CH4·8H2O中碳、氢、氧原子个数比为1:20:8
答案：C
| 阅读理解。 | ||||||||
| You're in a bit of a dilemma standing in front of the produce section of your local supermarket. In one hand, you're holding a conventionally grown Granny Smith apple. In your other hand, you have one that's been organically grown. Both apples are firm, shiny and green. Both provide vitamins and fiber, and both are free of fat, sodium and cholesterol. The conventionally grown apple costs less and is a proven family favorite. But the organic apple has a label that says "USDA Organic". Does that mean it's better? Safer? More nutritious? Several differences between organic and non-organic foods exist. Become a better informed consumer for your next trip to the supermarket. The word "organic" refers to the way farmers grow and process agricultural products, such as fruits, vegetables, grains, dairy products and meat. Organic farming practices are designed to encourage soil and water conservation and reduce pollution. Farmers who grow organic produce and meat don't use conventional methods to fertilize, control weeds or prevent livestock disease. Here are other differences between conventional farming and organic farming:
The U.S. Department of Agriculture (USDA) has established an organic certification program that requires all organic foods to meet strict government standards. These standards regulate how such foods are grown, handled and processed. Any farmer or food manufacturer who labels and sells a product as organic must be USDA certified as meeting these standards. Only producers who sell less than $5,000 a year in organic foods are exempt (免除) from this certification. If a food bears a USDA Organic label, it means it's produced and processed according to the USDA standards. The seal is voluntary, but many organic producers use it. | ||||||||
| 1. The main purpose of the passage is ______. | ||||||||
| A. to promote the sales of organic food B. to inform people organic food is better for their health C. to persuade people to become informed consumers D. to compare conventional and organic foods | ||||||||
| 2. According to the passage, the conventionally grown apple ______. | ||||||||
| A. costs less but tastes worse than an organic one B. doesn't look the same as an organic one C. has proven itself acceptable by the family D. contains more fat, sodium and cholesterol | ||||||||
| 3. Which of the following methods belongs to organic farming? | ||||||||
| A. Using chemicals to kill insects and prevent disease. B. Using rotted plants as fertilizer to promote plant growth. C. Using growth hormones to speed up animals' growth. D. Using insecticides to reduce insects and disease. | ||||||||
| 4. From the passage we know the organic certification program _______. | ||||||||
A. is not meant for all producers of produce |