的
When describing a known entity with an adjective or a relative clause there is no need use the third person neuter pronoun 它 (tā) 'it'. Instead the adjective can used be used with 的 at the end.
Example:
香山远吗? (Xiāngshān yuǎn ma?) Is the Fragrant Mountain far?
庭远的。 (Tǐng yuǎn de.) It is quite far.
This equates to 它挺远。
Or similarly
多长时间了？ (Duō cháng shíjiān le?) How long has it being going for?
昨天晚上开始的。 (Zuótiān wǎnshang kāishǐ de.) It started yesterday evening.
This equates to
昨天晚上开始的头疼。 (Zuótiān wǎnshang kāishǐ de tóuténg.) The headache, that started yesterday evening.