请找出划线部分发音不同的一项。
—____ the workers are very tired, ____they keep on working. — They are great. We must learn from them.
If Tony_____ to the corner this weekend, Bob will join him.
Her husband is a great cook. So she can enjoy _____ food every day.
—Would you mind opening the window? —____. Look at the heavy haze (霾) outside.
It’s ____ useful book. And ____ book is popular with students.