求VerbVerb Tense Exercise 5、6 Simple Past / Present Perfect答案

求VerbVerb Tense Exercise 5、6 Simple Past / Present Perfect答案（括号后面撒）
VerbVerb Tense Exercise 5
12. Jonny, I can't believe how much you (change) since the last time I (see) you. You (grow) at least a foot!
13. This tree (be) planted by the settlers who (found) our city over four hundred years ago.
14. This mountain (be, never) climbed by anyone. Several mountaineers (try) to reach the top, but nobody (succeed, ever) . The climb is extremely difficult and many people (die) trying to reach the summit.
15. I (visit, never) Africa, but I (travel) to South America several times. The last time I (go) to South America, I (visit) Brazil and Peru. I (spend) two weeks in the Amazon, (hike) for a week near Machu Picchu, and (fly) over the Nazca Lines.
VerbVerb Tense Exercise 6
Since computers were first introduced to the public in the early 1980's, technology (change) a great deal. The first computers (be) simple machines designed for basic tasks. They (have, not) much memory and they (be, not) very powerful. Early computers were often quite expensive and customers often (pay) thousands of dollars for machines which actually (do) very little. Most computers (be) separate, individual machines used mostly as expensive typewriters or for playing games.