118 Art museums do not usually think of their collections as capital or consider the interest income that would be generated if a portion of the capital would have been invested in another form.

(C) be generated if a portion of the capital were

(D) be generated if a portion of the capital was（C）

why here should use "were" instead of "was"?

thanks.

对于一般现在时态的虚拟.

假設語氣 (與現在事實相反)

If S1 + ( Vpt / were ) ..., S2 + would + V

--> be動詞一定要用were