Why?

We use the passive voice when we don’t want to say who or what does the action. This helps us start sentences with the most important information, especially when we don’t know, it’s obvious, or we just don’t want to say. 

simple present: am/is/are + past participle

A museum   _____________ by thousands of tourists.

How many languages ___________ in London - apart from English?

Answers:

is visited
are spoken