What is the difference between 本来 and 原来?

Question

I was learning in a Mandarin class and I was kind of stumped on the use of "本来" and "原来" when filling in the blanks in a sentence. Here's my attempt to these questions (taken from 汉语口语速成: 基础篇 pp. 91-92):

1. 这儿____是个冰场，现在盖起了高楼。(My answer was "原来", the answer is can be both.)
2. 回国的日子____定在下月二十号，可是因为没有买到机票，就改到二十七号了。(My answer was "本来", the answer is "本来".)
3. 这盘虾炒得太咸了，虾_____的味道都没有了。(My answer was "本来", the answer is "原来")
4. 我找了你半天，____你在这儿呀。(My answer was "原来", the answer is can be both.)

There's no problem with the sentence #2 and #3. I got it right on the second sentence. I got it wrong on the third sentence, since I just know that "原来" can be used as an adjective, and the speaker already realized that the taste of the food is not good, hence my mistake.

What makes me confused is the answer of #1 and #4, is it true that either "本来" or "原来" correct in sentence #1 and #4? I thought only one of them can fit.

From what I understand from Chinese Grammar Wiki and some Chinese movies, my thinking is this:

I'm using “本来” when something unexpectedly happened, and the speaker doesn't realize until it happens. But if the speaker accidentally find out or realize the situation has changed, I should use “原来”.

Is my thinking true? If not, then on which case should I use "本来" or "原来"?

UPDATE: Here's another example I got from a movie:

丁鐺："你們晚上沒演出啊?"

藍雲："沒有，最近演白天，你一個人來?"

丁鐺："是的，本來我要去百代試音的，但是我弄錯了日期，是明天。"

The speaker use "本来" here, can it be changed to "原来"?

Answer 1

'本来' means 'original/ originally/ at first'

For example: "我本来不想去的" (originally, I didn't want to go )

'原来'(the truth from the origin) means 'actually' /as it turns out

For example:

"原来你不想去" (you actually/ don't want to go)/(as it turns out, you don't want to go)

"原来你沒錢去" (you actually don't have money to go)/ (as it turns out, you don't have money to go

'原本' = '本来'

For example: "我原本不想去的" (originally, I didn't want to go)

• 这儿(本来/原本)是个冰场，现在盖起了高楼。

• 回国的日子(本来/原本)定在下月二十号，可是因为没有买到机票，就改到二十七号了。

• 这盘虾炒得太咸了，虾(本来的/ 原本的)味道都没有了。(the original taste)/ 这盘虾炒得太咸了，虾(原来的)味道都没有了。(the actual taste)

• 我找了你半天，(原来)你在这儿呀。

Many people use 原来 instead of 原本 when they meant "originally" because they think 原来 and 原本 are the same

原本" = “本來” ; "原來 = 其實

Answer 2

In my opinion, 1,2,3 can be both. 4 should be filled with 原来.

原来 could be used when you don't know something and then you find it out all of sudden. For example, 原来是你啊！ 原来是你干的啊！ 本来 can't be used for this sense.

Most of time they are interchangeable.

In your update sentence, 本来 is preferable, and 原来 is not that good. But if you put 原来 in the middle (丁鐺："是的，我原来要去百代試音的，但是我弄錯了日期，是明天,) that will be ok. This might be because if you put 原来 at the beginning of an sentence, that sounds you have found something all of sudden, which you didn't know. But actually you want to convey the sense originally.

I guess the key might be they are interchangeable within a sentence, but not at the beginning of a sentence!

丁鐺："是的，本來我要去百代試音的，但是我弄錯了日期，是明天。

Update

I feel this dictionary definition are accurate:

本来

1. 原来，原先。

杨朔《京城漫记》：“这地方在北京南城角，本来是京城有名的风景区。”

2 . 原有的。

本来面目。

3 .指人本有的心性。

黄人《〈小说林〉发刊词》：“心理之辟，尤在昧厥本来。”

4 .表示理该如此。

本来就该这么办

原来

1 . 当初；未经改变的。

周而复《上海的早晨》：“阿英给奶奶提醒，立即退了回来，把脸盆放在床上原来的地方接水。”

2 . 副词。表示发现从前不知道的情况。

魏巍《东方》：“郭祥勉强睁开眼睛，原来担架停在一面悬崖下。”

I think this should help you a lot if you can understand those definitions in Chinese.