Science currently recognizes around 1.8 million species on Earth (out of an estimated five million to 30 million total species—the true total remains unknown).

目前科学界已经知道的全球物种大约有180万个（而根据推测，全球总共有500万到3000万个物种——实际上，地球到底有多少物种还不确定）。

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Total solar eclipse is a rare phenomena, the ancients as a result of unknown causes, was given to give a lot of solar mystery.

日全食是一种罕见的天象，古人由于不明原因，于是就给日食赋予了许多神秘色彩。

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One of the schemes adopts the integral equation with equivalent current as an unknown function, whereas the other USES the integral equation with total electric field as an unknown function.

一种方案采用以极化电流为未知函数的积分方程，另一种方案采用以总电场为未知函数的积分方程。

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In power since December, its new government has moved quickly to reform the labor market and cut public debts, but the total hole on the balance sheets of its banks has remained the big unknown.

CNN: Spain is bailed -- but questions remain

Unlike with a variable-rate, Western-style loan, the borrower knows from the start how much the total payments will be (though of course fixed-interest loans are hardly unknown in the West).

ECONOMIST: A reader debate on Islamic finance

While it is unknown exactly how many iPad Mini units have been sold, Apple did reveal that it sold a combined total of three million tablets when the Mini and the iPad 4 were released.

FORBES: Apple Created iPad Mini to Lead Foreign Markets