don't know, didn't know, hadn't known, are, were

—Hello! I ________ you ________ in London. How long have you been here?

predictive meaning

end-focus

coordination

parallelism

Why do most contemporary English grammarians adopt a two-tense system?

Explain the principle of proximity of concord with examples.

Using a tag question:

Let's do it together.

Using extraposition:

To wear a respirator mask when you're working with fiberglass might be a good idea.

Using discontinuity:

Excessive exposure to violence on TV is more harmful than expected to children.

Using cleaving for object :

He likes playing games most.