ESERCIZIO NUM: 2871 - CATEGORIA: verbi > past-simple present-perfect - DIFFICOLTA': ****
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Completa il brano con il PAST SIMPLE oppure il PRESENT PERFECT dei verbi tra parentesi.

Most of us think we can't live without our mobile phones. However, they(not / be) in existence for very long. The very first mobile phones(not be) mobile phones at all. They(be) two-way radios that people like taxi drivers and the emergency services(use) to communicate. They(not / have) much memory and they (not / be) very powerful. They (be) often quite expensive and customers (pay) a lot of money for machines which (do) very little. Technology(change) a lot since then. Mobile phones (become) powerful machines with very practical applications. Manufactures(create) phones that can take pictures, send messages, and surf the Internet. The simple mobile phones of the past(evolve) into sophisticated machines.