Mrs. Brown was much disappointed to see the washing machine she had _____ went wrong again.
It is believed that forest bathing ______ strengthen the immune system.
As long as the laws of nature ______, there will be tornadoes.
North Korea fired a long-range rocket last month, but the launch was reported ______ in failure.
Some scientists have questioned the theory ______ CO2 is causing dangerous global warming.
They studied what ______ since 2007 and found Australian electricity prices were among the highest in the developed world.