What is the primary language spoken in Montreal?

Today’s Marriott world of rewards question:

What is the primary language spoken in Montreal?

(0r What is the official language of Montreal?)

The answer is:

French

Some really interesting stuff (Good for your GK)

Montreal is second largest city in Canada and in the top 5 french speaking cities of the world.
Montreal is the 10th most clean city in the world according to a 2007 Forbes study.
Montreal is one of the 25 most livable places on earth.

So why French?

The three greatest colonial empires – Britain, Spain and France shaped the demographics of earth between 15th and 19th centuries. Whatever these powers controlled, still bears their influence. Have a look at the French colonial map and you’ll know why French is the dominant language in Montreal, Quebec, Canada.