That, which or who?

Target Language or Knowledge:

Fill the blanks below with "that", "which" or "who":
1. Cars _that_ are hybrids use less gasoline than cars _that_ aren't. 2. People _who_ exercise regularly are less likely to become obese. 3. Roses, _which_ are often brightly colored, are given as gifts on Valentine's Day. 4. Dogs, _which_ are sometimes referred to as "man's best friend", provide good company to people _who_ are lonely. 5. In 2011 there was a tsunami in Japan _that_ triggered a nuclear incident at Fukushima, _which_ was very bad news for local residents. 6. I have a friend _who_ is a concert pianist. He plays classical pieces _that_ are old but still popular. 7. A scientist has discovered a gene _that_ affects appetite. 8. There are many factors _that_ impact on a city's livability. 9. Iron ore, _which_ is found extensively in Australia, is used to produce steel _that_ is required to construct skyscrapers. 10. Boris Johnson, _who_ is the Prime Minister of the UK, held a press conference today _that_ was controversial. 11. I finished my last exam today, _which_ made me very happy. 12. Plants _that_ require lots of water are hard to grow in arid environments, _which_ is unfortunate if you live in a desert and like ferns.