"Threw under the bus" is a colloquial expression that means to betray or sacrifice someone for one's own benefit.
Idiom
If you've ever heard a native speaker say that's a piece of cake and wondered what cake had to do with anything — you've met your first idiom. English films, songs, and casual chat are full of these fixed expressions, and missing them leaves the meaning slightly off-kilter. Learning idioms in chunks is the fastest way to stop sounding overly formal.
An idiom is a fixed phrase whose meaning isn't built from its individual words. Kick the bucket (= to die), spill the beans (= reveal a secret), break a leg (= good luck). They have to be memorised as whole units; word-by-word translation almost always misleads.
C2 | Proficiency
If you can argue a point in English, then switch register to comfort someone, then crack a joke that lands — without thinking about which words to choose — you're operating in C2 territory. Most learners don't need to reach this level. The reason it matters is the opposite: knowing C2 exists stops you from setting it as the bar when B2 or C1 is more than enough for what you actually want to do.
C2 is the proficiency level — the highest on the CEFR scale. It means near-native control of idiomatic range, register-switching, irony, and complex written argument across any subject.
C1 | Advanced
If you've ever sat through a lecture in English, written a complaint letter, or argued a point in a meeting and come out feeling actually understood — not just tolerated — you've felt what C1 looks like. The level matters because it's where most universities, certifications, and skilled-work environments draw their language line.
C1 is the advanced level in the CEFR framework, demanding fluent and flexible language: inversion for emphasis, mixed and advanced conditionals, formal subjunctive, cleft sentences, and complex nominal phrases — all used appropriately across registers.
Difficulty: Hard
If easy and medium questions are clicking but you still feel exposed in real conversation or formal writing, you've outgrown the basics. Hard material is where the gaps you didn't know you had show up: the distractor that "sounds right", the rule that interacts with another rule, the case where context changes the answer. It's where genuine fluency is built.
The Hard difficulty tag marks upper-intermediate to advanced challenges — typically B2 and above. Interacting rules, edge cases, plausible distractors, and contexts that require genuine understanding rather than surface pattern-matching.