The correct answer is D. All of the above.
The Harmattan is a cool, extremely dry wind that forms over the Sahara and blows westward or south-westward to the Gulf of Guinea. It is a tertiary wind, which means that it is a wind that is caused by the interaction of two other winds. In this case, the Harmattan is caused by the interaction of the northeasterly trade winds and the southwesterly monsoon winds.
The Harmattan blows during the dry season from December to February. It is a very dry wind, and it can cause significant dust storms. The dust from the Sahara can be carried as far as the Caribbean and the Amazon rainforest.
The Harmattan is a major factor in the climate of West Africa. It brings cool, dry air to the region, and it can cause significant changes in temperature and humidity. The Harmattan also has a significant impact on agriculture and transportation in West Africa.