Core Verb and Preposition Combinations

Read this excerpt from the Superhero Academy's training manual. Select ALL the sentences that use the correct verb-preposition combinations.

- [x] You must concentrate on controlling your laser vision before lunch.
- [x] Many novices succeed in flying only after they stop worrying about gravity.
- [ ] Please refrain of using telepathy during written exams.
- [ ] The instructors apologize at the accidental teleportations yesterday.

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The correct sentences are **You must concentrate on controlling your laser vision before lunch.** and **Many novices succeed in flying only after they stop worrying about gravity.**
> Let's look at the core combinations:
> * **Concentrate** is followed by **on**.
> * **Succeed** is followed by **in**, and **worry** is followed by **about**.
> * **Refrain** should be followed by **from** (not *of*).
> * **Apologize** should be followed by **for** an action (not *at*).
