Paragraph NineLanguage learning

Paragraph Nine
Language learning is nothing new, but technology has made it easier than ever to grasp. The popularity of language-learning apps has boomed around the world, especially as more people are working or studying at home. They are usually easy to use because you can access them on your smartphone. And apps can offer languages not popular enough to be taught at evening classes or schools or universities.

Language-learning apps are c().
【正确答案】：convenient