In each of the following sentences, a preposition is missing. As he is an elderl...

Questão de Inglês da banca IBFC aplicada no concurso INEP (2012). Confira a resolução completa abaixo:

In each of the following sentences, a preposition is missing.

As he is an elderly man, he has a difficulty ________ using the computer. This is a simple method ________ searching suitable solutions. She was in trouble _________ robbing a car. The alternative that respectively brings the correct preposition for each one is