Why not both take it at the same time?

为什么不同时服用呢？

youdao

We can believe the molecular data, the DNA, or we can believe the skeleton trail, but unfortunately, not both.

我们可以相信分子数据和DNA，或者我们可以相信骨架线索，但不幸的是，我们不能两者都相信。

youdao

Most marine deposits from around the world contain either plankton or a lot of fern spores but not both together in the same layer.

世界上大多数的海洋沉积物不是含有浮游生物就是含有大量的蕨类孢子，但它们并不是同时存在于同一层中。

youdao

"Aylmer," said Georgiana, "I do not know what the cost would be to both of us to remove this birthmark.

VOA: special.2009.09.26

If he's not one but not the other,and if he's not both, the only other possibility is that he's neither.

如果他不是非此即彼，如果他不同时是两者，那么剩下的可能性就是，他两者都不是。

耶鲁公开课 - 死亡课程节选

So there's no claiming that things have to be one or the other, but not both.

因此并不能说,不是好就是坏而不能两者兼而有之。

耶鲁公开课 - 死亡课程节选

Government should tax either the value of an asset or its yield but not both.

FORBES: Capital Gains Tax is an Economic Monkey Wrench (2012)

Dividends are either taxed at the company level or at the individual income level: not both.

FORBES: Obama's Budget Raises Dividend Taxes to 39.6%: This is Not a Good Idea

Today's Internet-enabled set is either a bog-standard television or a sub-standard Web browser, but not both.

ECONOMIST: Web television