Learn Arabic (Modern Standard): كلتا الحقيبتين اللتين تركتهما في القطار فيهما مجوهرات ثمينة. - Both bags that I left in the train contain valuable jewelry.

In Arabic relative clauses, you usually need a resumptive pronoun (a pronoun that points back to the noun being described) if that noun is the object of the verb. In English, we just say "that I left," but in Arabic, you literally say "that I left them." Because we are talking about two bags, we attach the dual pronoun هما to the verb, making it تركتهما.

Where is the verb for "contain" in this sentence?

There is no direct verb for "contain" here. Instead, Arabic often uses a preposition with an attached pronoun to express possession or containing. The main predicate of this sentence is فيهما, which means "in them (two)." The core sentence is literally: "Both bags... in them (is) valuable jewelry."

Why do we use اللتين instead of the standard feminine التي for "that"?

Arabic relative pronouns must match the noun they refer to in gender, number, and case (for duals). Because الحقيبتين (the two bags) is dual and feminine, the relative pronoun must also be dual and feminine. Furthermore, because the noun is in the genitive case, the relative pronoun takes the matching genitive dual form اللتين rather than the nominative اللتان.

Why is الحقيبتين in the genitive/accusative case (ending in -ayn) when it is at the start of the sentence?