Read the following passage and mark the letter A, B, C, or D to indica

Read the following passage and mark the letter A, B, C, or D to indicate the correct word or phrase that best fits each of the (31) blank.

Birds are fascinating to many people, and bird watching is a popular hobby. The best time to watch birds is in the early morning, (31) ___ birds are usually very active at that time of day. The observer must keep still and quiet in order not to (32) ___ the birds away. If you live in a part of the world where migratory birds spend their breeding season, then you will have the (33) ___ to see nest-building activity. Over the ages, different species of birds have evolved with different types of nest-building skills. It makes an interesting study to (34) ___ the different types of nests built by birds and to watch them as they build their nests. After the breeding season is over and the babies have left the nest, it is time for the birds to head for (35) ___ parts of the world to spend the winter months. Birds navigate to their winter feeding grounds, using the stars or the sun as their guide.

• A. A. so
• B. B. because
• C. C. though
• D. D. but