The word “these" in paragraph 3 refers to ____________

I know it works in theory, but try putting it into ____________ and you'll find out it's failure.

Read the following passage and mark the letter A, B, C, or Don your answer sheet to choose the word or phrase that best fits each of the numbered blanks from 25 to 29  

     Humans are destroying the earth's tropical rain forests. About 80,000 square kilometers are being destroyed every year. About a quarter of the (25) ____________ comes from people cutting trees for fuel. Another quarter is to make grassland for their cattle. The (26) ____________ trees are cut down to sell the wood to start farms.  

     The population in cities all over the world is growing, and more and more wood is needed to build huge new buildings. For example, 5,000 trees from Sarawak rain forest in Malaysia were used to build just one tall building. (27) ____________ people continue cutting down that many trees in Sarawak rain forest, all the trees could be gone in eight years.  

     The world needs more food, and it (28) ____________ like a good idea to clear the rain forests and use the land for agriculture. Many people think that the land under these huge, thick forests must be in rich nutrients, but it isn't. This is another surprising thing about rain forests. Most of the land in tropical rain forest is very (29) ____________

Mont Blane, ____________ we visited last summer, is the highest mountain in Europe.

I should have asked her for a plan of the house. If I ____________, I would have found everything.

____________ the age of 21, he was able to gamble in Las Vegas.