GRE作文是中国学生比较头痛的，经常准备很多时间最后还是只得到3.5。我之所以得到6分，个人认为我的文风比较淳朴扎实，有科学性，写的思路比较广(正、反、特)，字数也比较多(I800+、A700+)。
The first problem with the argument involves the comparatively low incidence of depression
among our ancestors. The author assumes that no factor other than the ingestion of omega-3
is responsible for this lower incidence. However, it is entirely possible that environmental or
other dietary factors are instead responsible for the lower incidence. For example, perhaps
other substances common in the U.S. diet today, and which promote depression, were not part
of our ancestors' diets.
Another problem with the argument involves the low incidence of depression reported
among today's fish-eating societies. To reasonably infer a causal relationship between
fish-eating and low rates of depression in these societies, two assumptions are required. The
first is that the types of fish consumed in these societies in fact contain omega-3; however the
artide provides no evidence that this is the case. The second assumption is that the reported
incidence of depression accurately reflects the actual incidence. However, it is entirely
possible that in those societies people generally do not report depression.
A third problem with the argument is that it assumes that omega-3 is only available in fish.
However, the author provides no evidence to substantiate this crucial assumption. Perhaps
people can ingest omega-3 by taking fish oil capsules rather than eating fish. Or perhaps
omega-3 is also found in other foods as well. In either case, the author cannot reasonably
conclude that we must eat more fish to ingest omega-3 and thereby help prevent depression.
Finally, in concluding that people in the U.S. must ingest more omega-3 to prevent
depression, the author infers that this is the only means of prevenl~ag depression. This
reasoning is fallacious. There might be a myriad of alternative ways to prevent depression;
moreover, experience and common sense informs me that this is indeed the case.
In conclusion, the argument is unconvincing as it stands. To strengthen it, the author must
provide clear evidence that no other factors explain the comparatively low incidence of
depression among our ancestors. The author must also show that in modem fish-eating
societies people in fact ingest more omega-3 than people in the U.S. do, and that the
incidence of depression is in fact lower in those societies. To better evaluate the argument, we
would need more information about alternative methods of preventing depression and
alternative sources of omega-3.
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