题目内容：

It‟s no secret that American infrastructure is aging. Concrete(混凝土) structures, in particular, are in desperate need of repair.

Cracks (缝隙) are very common due to various chemical and physical phenomena that occur during everyday use, which can be quite harmful as they provide an easy route in for liquids and gasses and the harmful substances they might contain. But continuous repair work is difficult because it usually requires a huge amount of labor and investment. So since 2013, I‟ve been trying to figure out how these harmful cracks could heal themselves without human involvement. The idea was originally inspired by the amazing ability of the human body to heal itself of cuts, bruises and broken bones. In the same way, can we provide necessary products to concrete to fill in cracks when damage happens?

My colleagues from Binghamton University and I have found an unusual candidate to help concrete heal itself: a fungus (真菌) called Trichoderma reesei. We initially screened about 20 different species of fungi in order to find one that could stand the difficult conditions in concrete. Of all the fungi we tested, only T. reesei could survive this environment. Despite the sudden PHincrease, its spores (孢子) developed into threadlike things and grew equally well with or without concrete.

We propose including fungal spores, together with nutrients, during the initial mixing process when building a new concrete structure. When the unavoidable cracking occurs and water finds its way in, the sleeping fungal spores will start to grow. They then will work as an activator within the calcium-rich conditions of the concrete to promote precipitation (析出) of calcium carbonatecrystals. These mineral deposits can fill in the cracks. If cracks form again and environmental conditions become favorable, the spores could wake up and repeat the process.

Our research is still in the initial stage and there’s a long way to go to make self-healing concrete practical and cost-effective. But the scope of American infrastructure’s challenges makes exploring creative solutions like this worthwhile.

1.Why does the author mention the self-healing of human body?

A. To show how amazing human body is.

B. To prove everything will turn out to be fine.

C. To provide a possibility of concrete healing itself.

D. To stress that it’s unnecessary to have medicines.

2.What do we know about T. reesei?

A. It has been applied to building a new concrete.

B. It can bear the tough conditions in concrete.

C. Its spores will be useless after one repair.

D. It poses potential risks to environment.

3.What does the underlined word “this” in the last paragraph refer to?

A. The challenges of American infrastructure.    B. The research on self-healing concrete.

C. The process of cracking.    D. The promotion of spores.

4.Which of the following can be the best title for the text?

A. The Danger of Cracks    B. The Aging of American Infrastructure

C. The Most Powerful Fungus    D. Concrete Filling Its Own Cracks