下面短文中有10处语言错误，请在有错误的地方增加、删除或修改某个单词。

增加：在缺词处加一个漏词符号（∧），并在其下面写上该加的词。

删除：把多余的词用斜线（﹨）划掉。

修改：在错的词下划一横线，并在该词下面写上修改后的词。

注意：

1．每处错误及其修改均仅限一词；

2．只允许修改10处，多者（从第11处起）不计分。

Dear Grandpa,

How are you these days? I have been missing you very much after I went to college a year ago. Whenever I think of the old days, I feel very happily. I still remember when I was a child, you always held me in your arms and told me stories till I fall asleep. We often went to the fields to enjoy the pleasant view there. You told me the name of different plants and characteristics. Gradually, I became interesting in biology and chose to learn biology when I entered into the college. Now my friend Ann, together with me, are going to do field study and the findings will be use as materials for our research. Since we’ll do the study in our hometown,so I hope to see you then.

用t0和t1表示产生1.0密度值的无屏和有屏照射量，则增感率的表达式是（）

A.f=t0/t1

B.f=t1/t0

C.f=t0-t1

D.f=t1-t0

E.f=t0+t1