The correct answer is: Only I is implicit.
The statement is an advertisement for X brand shoes. It claims that X brand shoes are durable and available in all sizes. The advertisement is trying to persuade people to buy X brand shoes.
Assumption I is that normally people like durable shoes. This assumption is implicit in the statement because the statement is trying to persuade people to buy X brand shoes by claiming that X brand shoes are durable. If people did not normally like durable shoes, then the advertisement would not be very persuasive.
Assumption II is that very few people read advertisements in the newspaper. This assumption is not implicit in the statement. The statement does not say anything about how many people read advertisements in the newspaper. It is possible that many people read advertisements in the newspaper.
Assumption III is that very few people read the newspaper. This assumption is also not implicit in the statement. The statement does not say anything about how many people read the newspaper. It is possible that many people read the newspaper.
Therefore, only assumption I is implicit in the statement.