Using universal modus tollens, fill in the following

1. People who are good at logic make good programmers.
   Buffy would not be a good programmer.
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2. My professors are happy when I pay close attention to their lectures.
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     My professors are not happy today.
   
   
3. x, k  Z, if x = 2k for some integer k, then x is even.
   x is not even.
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4. Animals at the bottom of the food chain are very nervous.
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      Lions are not at the bottom of the food chain.