New words：

certainly ['sə:tənli] adv. 当然；肯定；无疑；确定

Sample Sentences：

They will certainly succeed.
I will certainly see you into the train.
I'm certainly never going there again.
"May I use your motorcycle? " "Certainly".
‘Do you think all this money will change your life?’ ‘Certainly not.’

New words：

certain ['sə:tn] adj. 肯定；确定；确信；无疑
make certain 弄确实；弄清楚；弄明白
for certain 肯定；确定；无疑

Sample Sentences：

We are certain to win the game.
I was certain that he had seen me.
There is no certain cure for this disease.
I can't say for certain when we'll arrive.
Please make certain when the train leaves.

New words：

malaria [məˈleriə] n. 疟疾

Sample Sentences：

Mosquitoes are carriers of malaria.
He fell sick with malaria on a trip to Africa.
There are many malaria sufferers in hospital.

New words：

ineffective [ini'fektiv] adj. 无效的；不起作用的；不奏效的
effectiveness [i'fektivnis] n. 效果；有效性；效能；效力；效率；成效
ineffectiveness [.inə'fektivnis] n. 无效；低效率；无能力

Sample Sentences：

An ineffective person should not be our leader.
The air-conditioner was ineffective in such a crowded room.
Scientists have carried out experiments to test the effectiveness of the new drug.

New words：

effect [ɪˈfekt] n. 影响；作用；效果；效应
effective [i'fektiv] adj. 有效的；生效的；实际的

Sample Sentences：

The drug has some bad side effects.
I can certainly feel the effects of too many late nights.

Window screens are effective in keeping out mosquitoes.
Their efforts to improve the production have been very effective.