Select the most appropriate option that can substitute the underlined words in the given sentence.
We should not underestimate the signification of female education.

To find the most appropriate option to substitute the underlined words "underestimate the signification", let us analyze the grammatical correctness and word usage of the sentence.

The sentence is: "We should not underestimate the signification of female education."

Here, the noun "signification" refers to the representation or meaning of a word, sign, or symbol. However, in the context of the sentence, the intended meaning is the quality of being important or worthy of attention (importance or consequence) of female education.

The correct noun to express this meaning is "significance".

Furthermore, the transitive verb "underestimate" directly takes the noun phrase "the significance" as its object without any preposition. Thus, "underestimate the significance" is grammatically correct and semantically appropriate.

Let us review the options:
1. underestimate the significance: Correct, as "significance" correctly denotes importance.
2. underestimate at signification: Incorrect due to the unnecessary preposition "at" and the inappropriate noun "signification".
3. underestimate on signification: Incorrect due to the unnecessary preposition "on" and the inappropriate noun "signification".
4. underestimate signification: Incorrect because it lacks the definite article "the" and uses the inappropriate noun "signification".

Therefore, the correct option that substitutes the underlined phrase is underestimate the significance.