What subject is your best? - Wat onderwerp is jouw beste?
What subject is your worst? - Wat onderwerp is jou slechtste / ergste?
What subject do you most like? - Wat onderwerp mag je best?
What subject do you most dislike? - Wat onderwerp vind je niet leuk?
I am good at Chemistry. - Ik ben goed in

I don't understand. - Ik begrijp niet.
Please speak slower. - Alstublieft spreek langzamer.
Would you write that down please. - Wou je dat even schrijven alstublieft.
Could you explain that please. - Kun je dat uitleggen alstublieft.
How is that pronounced? - Hoe spel je dat?
I have forgotten the word