The biggest obstacle which also slowed down nationalist activities in French West African Colonies was the

Analyze the question: It asks for the biggest obstacle that slowed nationalist activities in French West Africa. We need the factor that most weakened or delayed organized nationalism there.

Concept: France governed its colonies through assimilation. This policy aimed to turn educated Africans into "Black Frenchmen" by making them adopt French language, culture, and values. Those who qualified (the évolués) could become French citizens, especially in the Four Communes of Senegal (Dakar, Saint-Louis, Gorée, Rufisque).

Step-by-step reasoning:

1. Option A: assimilation policy. It encouraged the educated elite to identify with France rather than oppose it. Many of them saw themselves as French and sought equality within the French system instead of independence. Nationalism was therefore delayed and diluted. It also used direct rule, which undermined traditional African institutions. This fits well.

2. Option B: constitutional reforms and entrenchment of human rights. Reforms such as those after 1946 did give Africans some rights and representation in the French Assembly. These were concessions, not obstacles, and they did not entrench human rights in a way that blocked nationalism. This is not the main obstacle.

3. Option C: assassination of chiefs. This was not a widespread or characteristic French policy. Chiefs were mostly used as agents of administration. This is incorrect.

4. Option D: deportation of Africans to France. There were some individual exiles and punishments, but deportation was not the major, systematic obstacle. This is incorrect.

Answer: The assimilation policy is the best answer, so the correct option is A.

Tip: For French colonies, link assimilation = direct rule = a "French-minded" elite, so nationalism was slower than in British colonies, where indirect rule and Western-educated elites pushed for self-rule. Remember the contrast: British = indirect rule, French = assimilation.