Valentina Tereshkova, orbited the Earth forty times before landed on June 19, 1963.??
Today I practice grammar which was about active and passive form, i.e.

1. Valentina Tereshkova, the first woman in space, orbited the Earth forty times before landed on June 19, 1963

I have practice about that one yesterday and the sentences are:

2. Positioned at the top of the food chain, the Bengal tiger of southern India has no predators except man.

3. Resembling a skunk, teledu is a small, flesh-eating animal which is found is Java, Borneo, and Sumatera.

I got answer from Su.Ki on the two last sentence. [http://classic.italki.com/question/344709]

But, when I find a wrong word on the first sentence, I got lost I made a mistake again..hmmm

Why?

Maybe I have more practice in active and passive form on the next days

Question

Valentina Tereshkova, orbited the Earth forty times before landed on June 19, 1963.??
Today I practice grammar which was about active and passive form, i.e.

1. Valentina Tereshkova, the first woman in space, orbited the Earth forty times before landed on June 19, 1963

I have practice about that one yesterday and the sentences are:

2. Positioned at the top of the food chain, the Bengal tiger of southern India has no predators except man.

3. Resembling  a skunk, teledu is a small, flesh-eating animal which is found is Java, Borneo, and Sumatera.

I got answer from Su.Ki on the two last sentence. [http://classic.italki.com/question/344709]

But, when  I find a wrong word on the first sentence, I got lost I made a mistake again..hmmm

Why?

Maybe I have more practice in active and passive form on the next days

Answer

"Valentina Tereshkova, the first woman in space, orbited the Earth forty times before landed on June 19, 1963"
=> Valentina Tereshkova, ... before she landed on June 19, 1963.
=> Valentina Tereshkova, ... before landing on June 19, 1963.

These two are the only ways to express the idea.

Not everything can be omitted with equal ease.  For example:
1. I took a shower before went out:  BAD!
2. I took a shower before I went out. ("before" is a conjunctive)
3. I took a shower before going out. ("before" is a preposition)

There seems to be no logical explanation why #1 is bad.  It is just the way English has developed.  
No English speaker will say it like that, so you just need to get familiar with the accepted ways.

Not allowing the subject to be omitted is not a universal rule, though.
For phrases connected with "and / or" it often happens.

- I'll do this last thing and wrap up (what I'm doing".
- He made a big contribution and is now remembered for it.
- He either misunderstood it or is willfully distorting the fact.