The word “this" in paragraph 2 refers to _____________

Even though she looks very young, she is twice older than my thirty-year-old sister.

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

GREEN ENERGY

     Fossil fuels are used to generate the majority of the world's energy, and they come in different forms.  For example, coal may be burned in a power (25) _____________ to generate electricity, but gasoline is burned in a car's engine to make it run. Neither of these two sources is considered green energy because they produce a lot of pollution when they are burned. In addition, they come from a source that is inevitably going to (26) _____________ 

     Green energy can be defined as any energy source that is to some degree nonpolluting. When it is called (27) _____________, this means that a person can replace the same amount of energy that was  consumed by that person (28) _____________ that person's lifetime. Since it look millions and millions of years to create the fossil fuels that we now burn, we know that they cannot be replaced by us.  

     Wind power and solar power, (29) _____________ harnessed properly, are two excellent sources of green energy. Once the necessary parts such as wind turbines to generate wind power and solar panels to create solar power have been produced, only the pollution from the production is left.

She _____________ with her brother when he broke her favorite toy.

I am writing to apply for the _____________ of interpreter, which was advertised on T. V last night.

Before you sign the contract, _____________ in mind that you won't be able to change anything later.