Main topics Natural Languange Processig $($NLP$).$

$1.$ What is Text classification on Natural Languange Processig $($NLP$)?$ details explaination with example

$2.$ What is Text summarization on Natural Languange Processig $($NLP$)?$ details explaination with example

$3.$ What is Question answering on Natural Languange Processig $($NLP$)?$ details explaination with example

$4.$ Example paper$/$jurnal that related with topics about Text classification, Text summarization & Question answering?