题目内容：

Dogs and humans have been living side-by-side for about 15,000 years, but there are tons of facts about dogs that perhaps we have never heard of.

Night vision

Dogs have good night vision. Their large pupils let more light in and the rods (视杆细胞) work better in poor light. But the biggest factor is the tapetum (反光组织), which reflect light at the back of the eye. Besides, dogs’ whiskers (胡须) also help them “see” in the dark because they pick up on very small changes in air, providing dogs with information about the size, shape, and speed of things nearby.

Secret tail code

Dogs can use their tails to communicate. They wag their tails to the right when they are relaxed or happy, and to the left when nervous or threatened. When they’ re aggressive, the tails will stick straight-up in the air. A broad wag is friendly while a slow wag is neutral, neither excited nor anxious.

Dreams

We often see a dog’s body making sudden movements in its sleep. Dogs have the same brain wave patterns as humans’ while they are asleep, so they dream just like we do.

Super nose

Dogs can find their way home despite long distances. Their noses are a vital part of their incredible sense of direction. The part of a dog’s brain that controls smell is 40 times larger than humans’. They’re able to follow smells for miles. Furthermore, dogs have an amazing ability to recognize the smells given off by the abnormal cells in human bodies, including cancer. This is something scientists are eager to explore further. And interesting, a dog’s “fingerprint” is on its nose. The patterns on dogs’ noses are so distinct that they can actually be used to identify the animals.

A sixth sense

Dogs act strangely before something bad, like a storm or earthquake, happens, for they are sensitive to low frequencies that humans can’t sense. So don’t let their strange behavior go unnoticed next time. It could save your life.

1.Which of the following indirectly helps dogs see well in the dark?

A. Their rods.    B. Their tapetum.

C. Their whiskers.    D. Their pupils.

2.If a dog holds up the tail, it indicates ________.

A. happiness    B. attack

C. friendliness    D. relaxation

3.What hasn’t been discovered about a dog?

A. Why it can sense natural disasters.    B. Why it has an acute sense of smell.

C. What emotions it shows with its tail.    D. How it can smell humans’ illnesses.

4.In what way are dogs like humans?

A. They dream when they sleep.    B. They have good night vision.

C. They have distinct nose patterns.    D. They can react to low frequencies.