English Language · Sentence Completion

In the question given below, a part of a sentence is given followed by three clauses. Choose the option containing the clause(s) that complete the sentence in a grammatically and contextually correct manner. The fintech startup's mobile application is not only simplifying cross-border remittances, ... I. but has also reduced the transaction fees by nearly forty percent. II. but nevertheless, it requires a stable internet connection for all users. III. but also ensures high-level encryption to protect sensitive financial data.