托福考试

【单选题】
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What aspect of butterfly development does the professor mainly discuss
A、The way in which adults alter their lifecycle to reproduce.
B、Their similarity to other holometabolic creatures.
C、Their transformation from caterpillars into adult imagoes.
D、The four specific phases they experience as they grow.
网考网参考答案：D
网考网解析：
[解析] 12-17 [Professor (female)] Good afternoon, everyone. Q12 Today we’re gonna discuss the development of butterflies and how--as I’m sure most of you already know--they progress through four distinct stages: egg, larva, pupa, and adult. It’s a rather unique lifecycle, one that sets butterflies apart from many other organisms. Um, you may not be aware of this, but there’s a term that describes this kind of lifecycle-- we call it "holometabolism." Q17 Holometabolism--literally meaning, um, "total change"--refers to the complete metamorphosis that occurs in organisms like butterflies, as they progress through the four stages of their lifecycle, starting as an embryo within an egg and ending as an adult imago... [Student A (male)] What was that you said...imago [Professor] Is that term new to you Imago. In insects, the imago is the last stage of development. In butterflies, it’s the stage where they become sexually mature and develop fully functional wings--the stage where they actually become a...a butterfly. Got it OK. Q13 So let’s just jump right into the topic then, starting with the stage of development where the butterfly is an egg. Uh, I think I’ll talk specifically about the lifecycle of monarch butterflies--to represent the lifecycle of butterflies in general. So, the whole process of development in monarchs--from egg to adult--takes about a month. It all begins when an adult monarch lays a single egg on the leaf of a milkweed plant. um, usually it’s on the underside of the leaf, near the top of the plant. We aren’t exactly sure how many eggs an adult female will lay during the course of her lifetime, but scientists suspect that it may be from 100 to 300. Anyway, after about four days, these tiny little eggs--they’re about a millimeter long--these tiny little eggs hatch. Q13 And once they’ve hatched, monarchs enter the larval stags. [Student A] Is this the stage where they’re known as caterpillars [Professor] That’s right. Q14(C) This is the stage where the monarch exists as a caterpillar-- caterpillars are butterflies in larval form. Q14(E) Um, you could basically say that caterpillars are little more than eating machines. That’s pretty much all they do--eat. Eat and grow, I should say. That’s because during the larval stage, butterflies do all of their growing. For two weeks, caterpillars just sit around on milkweed leaves and eat and eat and eat. Q14(B) Periodically, monarch caterpillars actually outgrow their skin! So they molt--that is, they lose their skin and grow a new one. At the beginning of the larval phase, monarch caterpillars are about 2 to 6 millimeters long, but by the end of it, they’re anywhere from 25 to 45 millimeters in length. [Professor] Q13 After the larval stage, the monarch proceeds into the pupal stage. Uh, let me show you some slides so you can see what this really looks like. So, uh, first here’s the egg...then, this one shows the larval stage...and here, this is the slide I wanted you to see. It’s in what we call the pupal stage. Quite a transformation, isn’t it [Student B (male)] That’s also got another name, right Uh...chrysa...chrysalis! [Professor] Right. It’s also called the chrysal 查看试题解析出处>>