-- _____is that used for?---_____ the floor.
To maintain a nice relationship, both sides are advised to focus on _________ they have in common.
After the disaster, the first thing the local government did was to provide _____ for the homeless families.
Most scientists seem to agree that ______ certain limit should be set on _______ consumption of cars to ease air pollution.
Helen devoted herself ________to her research and became a top scientist in the field of applied physics.
Vitamin D helps our bodies make a special chemical,and this special chemical, ______ affects our brains,making us feel happy.