London is a key test-bed for the UK hydrogen economy and also on Tuesday, the city took delivery of a dozen new zero-emission vehicles from Toyota , powered by hydrogen fuel cells made by UK-based ITM Power (LSE: ITM.L - news ) , while Mayor of London Boris Johnson also timed a visit to the Japanese headquarters of the car manufacturer on the same day.
Refer to the input text as context and select the correct relationship between 'Boris Johnson' and 'Mayor of London' from the available options.
Options: position held, distributed by, location of formation, stock exchange