With his son _____ , the old man felt unhappy.

 Mothers love children, which is a(n) _______fact in spite of cultural differences.

As there is less and less coal and oil, scientists are exploring new ways of making use of ____ energy, such as sunlight, wind and water for power and fuel.

She started laughing loudly when I began to sing，which made me feel very________.

The flight attendant welcomed us ___ the plane.