The question below consists of a set of labeled sentences. Out of the four options given, select the most logical order of the sentences to form a coherent paragraph.

P. They are on the market already but they are costly.

Q. Their cost depends on the sort you install and the size of your home.

R. These devices extract warmth from the air or the ground, or from water - a bit like a fridge operating in reverse.

S. Climate advisers anticipate that most homes in future will be warmed by heat pumps.

The correct answer is option 3) i.e. "SRPQ." 
Key Points

• In the above-mentioned paragraph, there is a chronological sequence of the sentences.
• Sentence S is the first sentence as it begins with the noun 'Climate advisers' and mentions climate experts predict that in the future, heat pumps will be used to heat the majority of homes.
• Sentence R is the second sentence as it begins with the pronoun 'These devices' in place of 'heat pumps' and mentions like a refrigerator running backwards, heat pumps draw warmth from the air, the ground, or water. Thus, it establishes a relation with the previous sentence.
• Sentence P is the third sentence as it begins with the pronoun 'They' in place of 'heat pumps' and further elaborates that heat pumps are already available in market, but they are expensive.
• The only option that shows such an arrangement is Option 3.
• Sentence Q is the last sentence as it begins with the pronoun 'their cost' and mentions that the type and size of your home determine the price of heat pumps. Thus establishes a relation with the previous sentence.
• Thus, the correct answer is Option 3.

The correct order is: 

S. Climate advisers anticipate that most homes in future will be warmed by heat pumps.

R. These devices extract warmth from the air or the ground, or from water - a bit like a fridge operating in reverse.

P. They are on the market already but they are costly.

Q. Their cost depends on the sort you install and the size of your home.