1．Before long,he____（forget） all about the matter.

will forget,"before long" 是指不就之后,表示将来
will be,in three hours 是三个小时后,表将来
is going to rain,前面的look at these clouds 是指看那些云,表示后面的要下雨是有迹可循的,有迹象的预测用be going to
will make,soon表示很快,将来
wil not take,在条件,时间和让步状语从句中,主句用一般将来时,从句用一般现在时表将来,if从句用的是一般现在时,所以主句就用将来时

1. forgot

2. will be

3. will rain

4. will make

5. will not take a

1.forgot 2.will be 3.is raining 4.made 5.will not take