London is considering a new airport on the Thames river estuary, which some people have called "Boris Island" after the current London mayor, Boris Johnson. U.K. Prime Minister David Cameron said "We (U.K.) need to retain our status as a key global hub for air travel. Not just a feeder route to bigger airports elsewhere, in Frankfurt, Amsterdam, or Dubai."

keep an eye on…

Hidetoshi: Let's go on the bridge and take photos of the river!

Jackie: You go ahead, I'll stay here and keep an eye on the luggage.

Explanation: to keep an eye on something means to stay near it and to make
sure that no-one bothers it or steals it. We also say often that we want
to keep an eye on our kids, or keep an eye on a person who is sick.

avoid strenuous activities

Doctor: After the surgery, you'll have to avoid strenuous activities.

Patient: Such as what?

Doctor: Well, don't lift anything heavy. And don't play football or rugby.
And instead of jogging, go for a slow walk in the park.

Explanation:  When we want patients to avoid stress on the body, we tell them to avoid strenuous activities.

leave it up to you

Dear Ken:

I understand that you want to organize the dental conference for next year. We said that the conference would take place in Asia, but we haven't decided the city yet. I'll leave it up to you. Whichever city you choose is fine.

Explanation: To leave something up to another person means that you are
giving them the power to decide, and not worrying too much about which choice they make.