A conversation at noon

Tenses and aspect are among the most difficult things to learn in any language, so I've made a pretty chart to simplify the whole thing. It includes an example of a conversation that includes each form at least once.

Click to enlarge!

UPDATE:
It helps if you look at which time phrases you can use with each form (left side of the chart). For example:

The race started at 10am. [the simple past]
The race has started now. [has is present tense, so it is about the past of the present (i.e., a time before now)]
The race had started at 11am. [had is past tense, so it is about the past of the past (i.e., a time before 11am)]

If it is now 12pm, you can't say:

WRONG: The race has started at 10am. [has is present tense, but 10am is in the past, so it doesn't make sense]

If you want to attach a time phrase to start instead of have, use the simple past form.

Prepositions and places: IN, AT, ON

The U.S. president lives in The White House at number 1600 on Pennsylvania Avenue in the city of Washington in the District of Columbia in the United States on Earth. If these are all places, why does English need three different prepositions (in, at and on) to introduce them? Fortunately, the answer follows from general rules about when each of these prepositions should be used.