The reading passage describes Hydropower facility which consists of a plant and a reservoir. The passage describes hydropower as a convenient source of energy. But the professor of the ecology class casts a doubt on this description of the hydro-power.
As the passage sites hydro-power as a convenient and environment-friendly source, the professor explains that water stored in dam may give rise to a situation such as flood. The flood may cause harm to the communities residing near the dam due to its adverse effects. The floods lead up to the accumulations of silts and toxic materials, which may produce toxic fumes. Thus by explaining it as not an environment-friendly source, the professor casts a doubt on the reading context.
He also gives example of the harm it may cause to the ecosystem near the reservoir. As the water evaporates, it cause decrease in the water level. This can cause the birds to have lesser insects as a part of their food. Fishes require a steady flow of water to sustain their life, the reservoir for the hydro-power plant, stops the steady flow of water, causing disturbance in the aquatic Ecosystem. This is another example by the professor; to cast a doubt on the fact that hydro-power is an environment-friendly source.
The professor even disagrees to the fact that hydro-power is relatively inexpensive. He states that the plant set up comes with a huge cost, making it rather expensive. He also argues that water may not be considered as a renewable source as it is dependent on various factors viz. natural conditions, etc.
To summarize up, the professor sites various examples to prove his reasons worthy to cast a doubt on the context given in the reading passage.
Don't need a conclusion paragraph.
better to have 4 paragraphs:
para 1: introduction
para 2: doubt 1
para 3: doubt 2
para 4: doubt 3
Read sample essays from ETS:
Don't repeat words or phrases like 'cast doubts'
Attribute Value Ideal
Score: 23 in 30
Category: Good Excellent
No. of Grammatical Errors: 0 2
No. of Spelling Errors: 0 2
No. of Sentences: 16 12
No. of Words: 288 250
No. of Characters: 1392 1200
No. of Different Words: 135 150
Fourth Root of Number of Words: 4.12 4.2
Average Word Length: 4.833 4.6
Word Length SD: 3.093 2.4
No. of Words greater than 5 chars: 91 80
No. of Words greater than 6 chars: 74 60
No. of Words greater than 7 chars: 48 40
No. of Words greater than 8 chars: 42 20
Use of Passive Voice (%): 0 0
Avg. Sentence Length: 18 21.0
Sentence Length SD: 5.579 7.5
Use of Discourse Markers (%): 0.438 0.12
Sentence-Text Coherence: 0.346 0.35
Sentence-Para Coherence: 0.571 0.50
Sentence-Sentence Coherence: 0.122 0.07
Number of Paragraphs: 5 4