Plants have to stand their ground when pests attack. Theres simply no running away. Some plants play defense， using prickly thorns， thick bark or even bitter tastes to ward off insects and other attackers. But for many plants， the best defense is a good offense. These plants - including some varieties of corn and cotton - call for help. And predatory critters frequently respond， arriving to prey on the plants attackers.

Of course， plants dont literally scream out to those helpers. Instead， they produce chemicals known as volatiles. Such chemicals easily evaporate and travel on the wind. The odor of these vapors silently attracts insects or other helpers - organisms that scientists call "bodyguards".

Bodyguard critters eat the pests that eat plants. So if plants have enemies， then bodyguards are enemies of the plants' enemies.

Plants evolved the ability to produce these chemical distress calls long ago. Scientists only discovered this secret signaling， however， in 1988. Since then， researchers have been probing how plants use these chemicals to communicate with animals. Their surprising findings have begun helping farmers boost the amount of crops they produce - and they do it with less need for toxic pesticides.

植物天敵的天敵

植物受到害蟲攻擊時無法逃離，只能呆在原地。有些植物憑借荊棘、厚皮甚至苦味來驅(qū)走害蟲和其他攻擊者，達(dá)到保護(hù)自身的目的。但對于許多植物來說，最佳防御手段是強(qiáng)有力的進(jìn)攻。此類植物，包括玉米、棉花的某些品種，它們會發(fā)出求救信號，害蟲的天敵通常會作出回應(yīng)，前來捕殺攻擊植物的害蟲。

當(dāng)然，植物不是真的向救援者發(fā)出尖叫聲，而是釋放出具有揮發(fā)性的化學(xué)物質(zhì)。該化學(xué)物質(zhì)很快蒸發(fā)，并隨風(fēng)飄散。蒸發(fā)霧氣的氣味會悄然引來昆蟲或其他救援者，科學(xué)家將這些救援者稱為“保鏢”。

被稱為“保鏢”的小動物會吃掉吃植物的害蟲，所以，如果植物有天敵，那么植物保鏢是植物天敵的天敵。

很久以前，植物在進(jìn)化過程中就已經(jīng)獲得了這種釋放化學(xué)物質(zhì)來求救的能力，但是科學(xué)家在1988年才發(fā)現(xiàn)了這種秘密求救信號。自那以后，研究者們開始探究植物怎樣利用化學(xué)物質(zhì)與動物交流，他們驚人的研究發(fā)現(xiàn)已經(jīng)開始用于幫助農(nóng)民增加作物的產(chǎn)量，并且?guī)椭r(nóng)民們減少了對有毒殺蟲劑的依賴。

（注意斜體字的譯法）

If your wallet's starting to get a little too thick to fit in your pocket， a new gadget named Coin might be able to lighten your load. Remember， it's Coin， not coins.

It looks no different than a standard （1） c card， but is actually a small （2） d that can act as a credit card， debit card or gift card. The device is available for pre-order and expected to start shipping this summer.

Coin CEO Kanishk Parashar said that the company was born from the ashes of the failed company Smart Market. Coin isn't another system of （A） p ， but Parashar's way of uniting several different （3） m of payment into a single device. Coin users plug a magnetic strip reader into a smartphone， swipe heir cards， and sync their information through the company's app.

In order to make a payment， users tap a button on the Coin card and pick which account they want to pay with， whether it's a business credit card or a personal debit card. After picking an account， the Coin card is swiped through， no different than any other card.

It may seem a little risky to keep all your financial accounts bound to a single card. However， Parashar and his colleagues have engineered （B） s measures into Coin. All communication between the Coin card， app and servers are heavily encrypted. "All your financial information would be secured，" said Parashar.

In addition， Coin cards themselves broadcast a low-power Bluetooth signal that （C） d where your smartphone is. "It works on the concept of being on a leash，" said Parashar. "If you're walking away from your card and go out of range of the Bluetooth， your phone will then set an （4） a ."

But even if you miss that alert， you don't have to worry about other people using your card. After a certain period of time （determined by the user）， Coin will automatically deactivate and stop other p________ （people） from using it.

（A， B， C， D FOR CROSS， 1， 2， 3， 4 FOR DOWN. The first letters of the absents were given）

Horse Friends - Math Puzzle

Three horses are standing in a triangular field， which is exactly 100 yards on each side. One horse stands at each corner； and simultaneously all three set off running. Each horse runs after the horse in the adjacent corner on his left， thus following a curved course， which terminates in the middle of the field， all three horses arriving there together. The horses obviously ran at the same speed， but just how far did they run？