It's neccessary to be prepared for a job interview.Having th

1.It's+adj+ for sb to do sth 对某人来说做某事很…… it 在句中是形式主语,真正主语是to do sth
It's neccessary to be prepared for a job interview.该句中“to be prepared for a job interview”是真正主语,翻译为“面试前做好充分准备是非常必要的”.
2.动名词做主语,be of +n.=be + adj
翻译为“提早准备好答案将会非常有帮助.”