it's one word 所给的 = given

对方所给的两个选择项 = 对方给的两个选择项 The "所" is optional here. This structure corresponds to "sb/sth that/which/who + verb" in English. In such a structure in Chinese, "所" can often, though not always, be added before the verb. This doesn't make any difference to the meaning of the expression/sentence. It should be noted that if the verb is followed by two objects, "所" can't come before the verb. For instance, "对方所给你的两个选择项" sounds rather weird. And what's more, in everyday Chinese, people do not usually use 所 in a structure like 对方给你的两个选择项. Hope my explanation in English is intelligible to you.

“”“在汉语中 有时 “还是” 用在问句里询问的是对方对所给的两个选择项会做出什么选择。”“” There are many chinese words starting with 所. 所给 所提供 所给予 所谓 所取得 所以 所能 所表现 ...... 所 doesn't has specific meaning. I think it's a surpportive character. If you remove it from sentence, most chinese can also understand you. If you still need an meaning, I say it represents a directional relation, from object to subject. Othere examples: 中方对美方所提供的帮助表示感谢. 我对这次活动中你所给予的大力支持表示诚挚的谢意. 中方对美方在该项目中所取得的巨大成就表示赞赏. 中方对所谓的中美网络战传言表示不屑. 中方对尼克松总统在开启中美建交中所表现出的勇气表示钦佩. 在此时事件中中方所能做的仅限于人道主义范围内的援助活动.

所 means so So give (给) you So the reason of your use for your purpose. So what 所 所以呢? 所以什麼呢? So obtain that So get that So ..... so many .... So can do it... I eat the apple so (where from) ( original places) ( reason) sold by this shop or market- in Chinese translation straightaway .

”所“ 与后面的动词结合，构成名词性结构 我直接在百度百科里搜的”所“字，感觉用法应该是助动词的第一条或者第二条。