早晨的雾气如此稀薄，几乎感觉不到它的存在。

The morning mist was so ___unsubstantial that it seemed almost intangible.

她的指控毫无根据，缺乏任何具体证据。

Her accusations were ___unsubstantiated and lacked any concrete evidence.

他的借口听起来很空洞，没有任何实质内容。

His excuse sounded ___unsubstantiated and lacked any real content.