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Escribe una oración de conclusión. La oración de conclusión de tu párrafo debe relacionar todo. Una buena oración de conclusión reforzará la idea descrita en tu oración principal, pero ahora contará con todo el peso de la evidencia o los argumentos indicados en las oraciones de sustento. Después de leer la oración de conclusión, el lector no debe tener ninguna duda sobre la exactitud o la relevancia del párrafo como una unidad.

Más típico del español sería simplemente: Conclusión.

Aunque "oración de cierre" u "oración final" suena más natural, la definición no parece referirse tanto una terminación cualquiera, sino a una conclusión. Por tanto, creo que sería más preciso traducir "concluding sentence" como "oración (o frase) de conclusión".

Aquí hay otra explicación del término:

"Concluding Sentence

The topic sentence and the body now completed, it remains only to end the paragraph. This is accomplished through a "concluding sentence," essential to the stand-alone paragraph. The purpose of this concluding sentence is two-fold: (1) to reiterate the main point developed by the body sentences and (2) to signal the reader that this is the end of the paragraph. The concluding sentence for a stand-alone paragraph should accomplish one of the following:

(a) Restate the topic sentence of the paragraph
(b) Summarize by referring to the key points in the paragraph
(c) Draw a conclusion based on the information set forth in the paragraph
(d) Offer a final observation about the controlling idea
(e) Make a prediction based on the details of the paragraph

The concluding sentence often begins with a transition word to signal the reader. Here are some examples of transitions used with concluding sentences:

all in all
in other words
in any event
in brief
in short
therefore

In addition to the concluding statement, the writer may wish to include a "final thought." The final thought is the last sentence of the stand-alone paragraph. If the writer has not had an opportunity to interject an opinion about the topic, the final thought is the last opportunity to do so. The following is an example of a concluding statement and final thought:

You can gain both muscle and stamina if you follow these simple steps. Although any exercise program takes time, the results are bound to please.

The first sentence of the pair is the concluding statement, which reiterates a general statement about exercise and the steps to follow in order to achieve muscle and stamina. The last sentence is the writer's opinion about the results of such a program."