he years, people have learned from ants that teamwork and perseverance are indeed two key ______ to success.

What a fine day today!—Yes, but it is____ than yesterday.

ass doors have taken the place of thewooden ones at the entrance,_____ in the natural light during the day

It’s said that ______ of the water around the world______ polluted.

_____ they believe enjoying a sports team is a good way ______ new friends, I would like to attend community activities to widen my social circle.