解决这个问题首先要确定188c 的资产要求是一个在获邀时候就要达到的要求还是在移民局下签时候的要求。
移民法只是在188.252这个地方提到了
(1) The applicant has made, on or after the time of application, a complying significant investment (within the meaning of regulation 5.19C as in force at the time of application) of at least AUD 5 000 000.
但是在移民局政策指南3.9.16. The Statement of assets and liabilities (SALP)这里提到
Significant Investor stream applicants are required to provide evidence that the applicant and/or their spouse or de‑facto partner own net assets of a minimum of AUD5 000 000 at the visa application date and which are proposed to be used to fund the complying investment.
移民局在这里的规定是没有法律依据的。移民法并没有要求申请人在签证申请申请188c的时候就拥有500万澳币，移民法说的是on or after the time of application, 也就是说在递交签证申请前和签证下签前这个时间区间里任何时候，按5.19C的规定的方式投资500万就可以满足条件。
结合移民局政策指南3.9.17.4 对于申请中来源不明的资产的处理方式
Should there remain reasonable suspicions that the assets are not legally owned, officers may exclude these assets from their calculations. If the exclusion of an asset results in the refusal of a visa, any such strong and reasonable suspicions must be fully documented.
移民局对于来源不明的资产的处理方式，并不是全盘否定，而是只是把不能确定资产来源的部分剔除，其他还可以继续使用。
再结合移民局政策指南3.9.17.6对于赠与资产的处理方式。
…
- in most instances, where the relationship between the person gifting the funds/assets and the receiver of the gift is not of a parent/child relationship, it will not be accepted that the purported gifting arrangement is one with no obligation to pay back
…
- the person gifting any loans borrowed from a financial institution must own the security over which the loan is pledged.
…
父母是可以赠与子女资产办理188c 的， 父母也可以把房产抵押给银行套取现金来赠与现金资产。
同时移民局政策指南22.4 Funds unencumbered 规定
… If funds are borrowed by an applicant using a different asset as security for the loan, the funds themselves would be unencumbered for 188.246(2)(a) purposes…
所以从银行贷款来的钱是可以满足unencumbered 的规定的。
Reg 5.19C 规定
(3) All funds used to make the investment must be unencumbered and lawfully acquired.
这是和188.246 规定的
The funds used to make the designated investment mentioned in subclause (1) were:
(a) unencumbered;
是一样的词汇。
所以碰到资产无法解释的时候，188C申请人可以考虑让父母套现房产来继续申请，而不是撤销签证。这种方法应该也是几种解释资产来源可选方案中成本最低的。