划线部分的解释，与 alternative的关系是什么，没看懂

问题如下：

Identify three potential concerns regarding using alternative investments in Green’s personal portfolio

选项：

解释：

Liquidity concerns: Green has stated liquidity needs with a vacation home, college expenses, and possible down payments for his daughters in addition to retirement income. Alternative investments can have long lockup periods, making the funds unavailable for upcoming liquidity needs.

• Scale: In general, personal investors tend to have smaller portfolios, which can result in a concentrated asset class, leaving an imbalanced portfolio.

• Time horizon: Green is about five years from retirement, and alternative investments can have longer time horizons and may be inappropriate for a shorter timeframe.