Before revision:  There are two families of solutions to this challenge. One family of algorithms, namely retriever-readers, first retrieves some pieces of text that are probably relevant to the question, and then feeds the retrieved text to a neural network to get the answer.
After revision:  There are two families of solutions available: retriever-readers, first retrieves some pieces of text that are probably relevant to the question, and then feeds the retrieved text to a neural network to get the answer.