1 . 用方框中所给单词的适当形式填空。每词限用一次。

model       twelve       invent       free       whether

1. My father sent me a watch as my ________ birthday present.
2. You are among friends here, so you can speak ________.
3. It remains to be seen ________ this idea can be put into practice.
4. Jack has enjoyed making battle ________ since he was 11 years old.
5. The US government ________ the Internet in the 1960s.