Which of the following can NOT be used assubject

Please tell me how the accident________.I am still in the dark. [ ]

Only when _____ the painting _____ decide whether the painting is worth buying.

ys, in some western countries, coffeeis ____ most popular drink, while tea comes ____ second.

Hi，Michelle， I can’t find my e-dictionary.— Sorry，I it.I guess I put it on the top shelf with my things.