46.
(A) allegation
(B) infusion
(C) elation
(D) obligation

People can experience both elation and depression in a very short period.
人們可以在很短的時間內同時經歷興高采烈和沮喪。
(A) allegation
a statement, made without giving proof, that someone has done something wrong or illegal
（未經證實的）指責，指控
Several of her patients have made allegations of professional misconduct about/against her.
Allegations that Mr Dwight was receiving money from known criminals have caused a scandal.

(B) infusion
the act of adding one thing to another to make it stronger or better
注入；灌輸
An infusion of $100,000 into the company is required.
a drink made by leaving tea leaves or herbs in hot water
（熱水）泡制
She drinks an infusion of herbs.

(C) elation
a state of extreme happiness or excitement
興高采烈；喜氣洋洋；歡欣鼓舞
There's a sense of elation at having completed a race of such length.

(D) obligation
the fact that you are obliged to do something
義務；責任；職責
If you have not signed a contract, you are under no obligation to (= it is not necessary to) pay them any money.
You have a legal obligation to (= the law says you must) ensure your child receives an education.
something that you must do
必須要做的事情
I don't have time to do his work for him - I have too many obligations as it is.


資料來源：劍橋辭典