The rate applicable to taxable transactions shall be that in force at the time of the chargeable event.

However, in the following situations, the rate applicable shall be that in force when VAT becomes chargeable:

(a) 

in the cases referred to in Articles 65 and 66;

(b) 

in the case of an intra-Community acquisition of goods;

(c) 

in the cases, concerning the importation of goods, referred to in the second subparagraph of Article 71(1) and in Article 71(2).