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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _gen_explain_command( coll, spec, projection, skip, limit, batch_size, options, read_concern):
 """Generate an explain command document."""

    cmd = _gen_find_command(
        coll, spec, projection, skip, limit, batch_size, options)
    if read_concern.level:
        return SON([('explain', cmd), ('readConcern', read_concern.document)])
    return SON([('explain', cmd)])