There are a _______________ of ways to learn English, from YouTube to real-life discussions. Listening to people speak is one of the ____________ methods. When we listen to people speaking in English, we learn how to _____________ sentences and expand our vocabulary.

Let us discuss all options to understand them better. In option A, hardly cannot be used as it is followed by the word ‘of’. Also, the word futile is out of context here. In option B, using ‘too many’ will make the sentence grammatically incorrect as it is followed by ‘of’. Also, the third word, ‘drop’ does not add any meaning to the sentence. In option C, abundant is grammatically incorrect as it is followed by 'of’ and preceded by ‘a’ instead of ‘an’. Also, the second word useless makes the sentence sound wrong. Let’s move to option D. Here, the word plethora means plenty. Effective is grammatically correct and the word ‘construct’ adds meaning to the sentence. Thus, we will choose option d. The correct sentence will be - There are a plethora of ways to learn English, from YouTube to real-life discussions. Listening to people speak is one of the effective methods. When we listen to people speaking in English, we learn how to construct sentences and expand our vocabulary.