​I have to see a doctor because I have A STOMACHACHE.

Countable Ailments: ​
a fever / a sore throat / a cough / a runny nose / a headache / an earache
/ a stomachache...

Jane looked up IN SURPRISE when I shouted.

In surprise = 惊讶地 (adverb phrase)

His grandfather has been DEAD for more than ten years.

dead = adjective, used before a noun / after "be" e.g. The dead man / He is dead.

died = verb - simple Past / V3
e.g. He died last year. / He has died.

The song was so ENJOYABLE that she did not hear the telephone ring.

enjoyable = adjective of "enjoy" 令人愉快的

My neighbour USED TO be a doctor, but now he is a businessman who sells health supplements.

used to = 以前是 + Bare-infinitive (V1)

be used to = 习惯于 + Gerund (v + ing)
e.g. He is used to staying up late.

EATING too many sweets is bad for your teeth.

Subject = Noun / Gerund (v+ing)

I think you had better REPORT this matter to the police.

had better / 'd better = 最好
+ Bare-infinitive (V1)

DOES your brother speak English well？

Simple Present (Question Form):
Do / Does (subject) + V1

The girls in the class always cooperate with ONE ANOTHER.

one another = 多个之间
each other = 两个之间
e.g. The two girls had not known each other until last year.

Who is THAT lady sitting beside Ms. Eng?

that = 那一个 + Singular Noun
those = 那一些 + Plural Noun
e.g. Those ladies live and work in New York.