2. The bullet trains in Japan are.......! They go at more than 300 kilometres an hour.
a. such fast – Wrong – we use 'so' with adjectives like 'fast'.
b. such quick – Wrong - we use 'so' with adjectives like 'quick'.
c. so fast – Correct – this means the trains go very quickly.
d. so quickly – Wrong – we use adjectives with 'so'. 'Quickly' is an adverb.