Choose the correct expression in the following sentences

[blank_start]Until/When[blank_end] he arrives, everyone must stand.

We're not going to stop digging [blank_start]until as soon as[blank_end] we find the ancient ruins.

They're going to check the building [blank_start]before[blank_end] the President arrives.

Those flowers will be in bloom [blank_start]immediately[blank_end] spring comes.

Please phone your dad [blank_start]by the time[blank_end].

[blank_start]When[blank_end] the Smiths arrive, ask them to wait outside my office.

[blank_start]As soon as[blank_end] you hear the alarm, run for the exit.