角膜是一透明组织，它的形状是（）
A.横椭圆形
B.竖椭圆形
C.圆形
D.类圆形
参考答案：A
–Why has Tom looked unhappy recently?
–He has some difficulty ______ with his new classmates at school.
A．getting over
B．getting in
C．getting along
D．getting down
一氧化碳无色无味，比空气轻，易于燃烧，燃烧时呈（）火焰
A、黄色
B、蓝色
C、红色
