The fact has worried many scientists _____ the earthis becoming warmer and warmer these years.

Water is offered at the tourist attraction , so you _________ carry any.

3D printers are still _____ expensive for most of us ______ afford.

Not until all the fish died in the lake __________ how serious the pollution was.

The reason_________ he didn’t come was _________ he had to take care of his sick mother.