The maths problem is ______ hard for us ______ solve.

There are some birds singing ___ the trees.[ ]

Mary, is that umbrella ______?— No. It belongs to Jane.

We _______ many roses in the garden since last year.

Teterboro is the same airport where a plane took off earlier this morning before colliding (碰撞)with a sightseeing helicopter over the Hudson River.