Помогите плиз...очень срочно надо...

1)Условное обозначение на чертеже выпуклой,вогнутой линзы.

2)Ход лучей в выпуклой и вогнутой линзе.

рабочим надо сделать 3600 деталей один рабочий может сделать эти детали за 20 часов а оба рабочих вместе работая могут их сделать за 12 часов за сколько часов может сделать все эти детали второй рабочий

Mind the Gap Mind the Gap" is not just an announcement that you'll hear in the London Underground when a train arrives at a station. Much more than just a warning about the "gap" between a carriage and the platform, it's a phrase that has entered popular culture and has become synonymous with London. People who have visited England's capital city say "Mind the Gap" to each other — often accompanied by knowing glances and subtle nods — while the rest of the world wonders what they are on about. The phrase originated on the Northern Line, where the gaps between the curved train platforms at Embankment Station and the train itself were particularly large. The biggest gaps one needs to mind are at Bank Station on the Central Line and at Waterloo Station on the Bakerloo Line. Basically, early in the history of Tube-line building the companies had to build their railways beneath public roads, so sharp curves were required at some points. Probably, the gap at Bank Station is so large because the tunnel diggers of the time had to turn from side to side a lot to miss the Bank of England's vaults. One of the funniest urban legends about "Mind the Gap" is as follows: Once you are on a train platform, beware! Approaching trains sometimes disturb the large Gappe bats that live in the tunnels. The Gappes were brought to London in the early 19th century by French smugglers and have proved impossible to get rid of. The announcement "Mind the Gappe!" is a signal that you should cover your hair and look Itowards the ceiling. Very few people have ever been killed by Gappes, though, and they are considered only a minor drawback to an otherwise excellent means of transport. Ответить на вопрос: 1) What does the phrase mean when you hear it in the Underground?

Умоляю. Английский. 8 класс, нужно только первое задание. Зарание спасибо