[译] 他明天不能来。
[误] He will be unable to come tomorrow.

[正] He will not be able to come tomorrow.
[注] be unable to 多用于一般现在时或一般过去时。如：Some days she was unable to shake hands. 有几天她不能握手。A newborn baby is unable to walk or talk. 新生婴儿不会走，也不会说话。not be able to 可用于过去时、将来时及完成时等。如：Kitty was not able to see the difference between them. 基蒂当时看不出它们之间的区别。/I shall not be able to finish the work the day after tomorrow. 后天我完成了那件工作。/They have not been able to fulfill the task. 他们未能完成那项任务。