Learn Arabic (Modern Standard): ثالثا، المواصلات في المدينة سريعة. - Third, the transportation in the city is fast.

The word ثالثا means "thirdly" or "third." In Arabic, adding the "-an" ending to ordinal numbers turns them into adverbs used for listing points, just like adding "-ly" in English to say "firstly," "secondly," and "thirdly."

Why is the adjective سريعة (fast) in the feminine singular form?

The adjective سريعة describes المواصلات (transportation). Even though transportation is a plural noun in Arabic, it refers to a non-human thing. A major rule in Arabic is that non-human plurals are treated grammatically as feminine singular, so any adjectives describing them must be feminine singular too.

The word المواصلات ends like a regular feminine plural, but it translates to the singular English word "transportation." Why?

You spotted the ـات plural ending! In Arabic, the concept of transportation or public transit is expressed in the plural (literally "connections" or "links"). You will often see this where English uses a singular uncountable noun, but Arabic uses a plural countable noun.