Tim will not join our dinner tonight. Tim is going to deliver a speech in English on stage and sit for an open examination next month. Those're parts of the reasons that he needs to brush up hard in English.

1. For the above writings, should I say

a. parts of the reasons
b. part of the reasons
c. parts of the reason

2. Should I say

a. deliver a speech
b. present a speech

3. If there are more than one speech, should I say

a. two speeches
b. two speech

4. Any other mistakes I have made that I should take note of to make the sentences better?

Thank you.