简述如下：1. 预测未来（即纯粹将来时）时，可用will/shall, 或者be going to,但不能用现在进行时:Do you think it will / is going to rain this evening ? 你觉得天会下雨吗？（但不能说：... it is raining this evening?）2. 表示已经决定的事情（现在将来）时，用be going to 和现在进行时，一般不用will/shall:She is going to have a baby in June. 她六月要生孩子。或者：She is having a baby in June.（但不能说：... She will have a baby in June.）3. 表示现在能肯定将会发生的事情时，一般用be going to:Look at these clouds. It is going to rain.看看天上的云彩，要下雨了。4. 谈到条件时（如if），用shall/will对未来进行预测，但一般不用 be going to:If you come out for a walk, you will feel much better. 要是你出来散散步，你就会感到好多了。（但不能说：If you ..., you are going to feel much better.）即使条件没说出来，仍应按条件句对待：Come out for a walk, and you will feel much better. 要是你出来散散步，你就会感到好多了。5. be about to表示“快要，正要，马上就要”：Don't go out now---we are about to have lunch. 不要出去了，我们马上就要吃午饭了。I was about to go to bed when there was a knock at the door.我正要睡觉，忽然听到敲门的声音。在美国英语里，not about to表示“不愿意”：I am not about to pay so much money for a dress like that. 我不愿意或这么多钱买这样一件衣服。
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