1.Theoretically, a line can extend into infinity.

1.从理论上来说直线以限地延。

2.It is impossible to count up to infinity.

2.能数到穷大。

3.In this weather the cliff face was a foggy drop into infinity.

3.在气条件下，雾蒙蒙的悬崖隐入广漠限之中。