1 . 碧空如洗的秋天是用望远镜观察这类老鹰习性的最好时节。(when)(汉译英)

2 . By the closing decades of the 19th century, the hardwood forests ________ passenger pigeons nested had been damaged by Americans’ need for wood, which scattered(驱散)the flocks and forced the birds to go farther north, ________ cold temperatures and spring storms contributed to their decline. （用适当的词填空）

4 . In mid-September, ________ their seedless white grapes ripen, local farmers are busy picking grapes to be transported to other parts of the country. (用适当的词填空)

5 . 春暖花开的四月是欣赏这个南方小镇美景的最佳时机。（when) （汉译英）