1. I am having a shower now OR I am taking a bath now.
You say “I am having/taking a shower now” if you are actually using a shower to clean yourself in the bathroom. Otherwise you say: “I am having/taking a bath now.”
2. Your sister is riding her bicycle now OR Your sister is playing with her bicycle now.
We usually say: “Your sister is riding her bicycle now.”
3. She goes to school by bicycle OR Every day, she goes to school by bicycle.
We say “She cycles to school.” You don’t have to add “every day” to the sentence, because it is understood from the tense (present simple) of the verb that this is something she does regularly.
4. Please buy the souvenirs for me OR to me.
You should say “Please buy some souvenirs for me.”. You don’t use the word “the” in this sentence, because there has not been any mention of “souvenirs” before.
5. I like to watch movies OR movie.
You should say: “I like to watch movies.” In English, when we make a general statement, we usually use the plural form of a noun.
6. Your father visited me yesterday OR Your father came to see me yesterday.
You can use either sentence. The first sentence is more formal than the second sentence.
7. He was reading the newspaper when the train stopped OR He was reading a newspaper when the train arrived.
The correct sentence is “He was reading a newspaper when the train arrived.”, because there has not been any mention of “newspaper” before.
8. I am having my lunch now OR I am eating my lunch now.
Both sentences are correct.
9. I was watching TV when the clock struck eight o’clock OR I was watching the TV when the clock struck eight o’clock.
We say: “I was watching TV when the clock struck eight.” You don’t use “the” when you say “watching TV”, but you can use or not use “the” in the phrase “on the TV/on TV), e.g. in the sentence: “My friend appeared on TV last night because she won a singing contest.” Also, we don’t add “o’clock” to the number of the hour when we say “the clock struck eight”. We can use “o’clock” when we are actually talking about the time, e.g. “He came at eight o’clock.”
10. I have received your letter OR I have already received your letter.
You use the first sentence when telling someone you have received his/her letter. You use the second sentence in a situation where, for example, the person who wrote you the letter is worried that you may not have received it. “Already” emphasises the fact that you have received it.
11. Does the golf course open OR Is the golf course open?
The correct question is “Is the golf course open?” The statement form would be “The golf course is open.” When the main verb is “is” or another “be” verb like “am”, “are”, etc. you don’t use the “do” verb in the question.