I forgot to include these other sentences.

1)They saw trading stations on the river bank consisting of just a broken-down building and a few white men occupying it.
2) Though the natives were like them, they felt frightened because they couldn’t understand anything about their huge primitive world.
3) About fifty miles from Kurtz’s station they saw a hut. When they got nearer to it, they found a massage on the firewood urging them to approach cautiously.
4)Marlow also found an old book about seamanship in the broken-down hut which had notes in code written on it. 5)The following morning Marlow ordered first to raise and then to lower the anchor because of the thick fog. Then the silence was broken by a sudden noise which stopped again shortly afterwards.
6) One of the cannibals standing near Marlow asked him to catch the natives because they would eat them. Marlow was not surprised by these words because eating people was their custom.
7) The voices stopped and the fog lifted. They set off again up the river. Suddenly Marlow looked away at the river and he could see a lot of little sticks flying towards them.
8) They were being attacked from the riverbank. The helmsman dropped the wheel and picked up a rifle. All of a sudden he dropped his rifle and fell at Marlow’s feet.
9) He had been wounded in his side by a spear. The blood ran over Marlow’s shoes. Marlow grabbed the wheel and steered towards the middle of the river.
10) The helmsman died soon afterwards. Marlow expected Kurtz to be dead as well. He is disappointed at the thought he would never hear Kurtz’s ideas.
11) He failed maths and English at the end of the second term. So he spent his summer holidays preparing for his make-up exam at the end of August.
12) I went to the seaside for my holidays (also during my holidays)
13) I introduced this year's program to the class and I explained them how to use their course-book. I find it difficult to make myself understood.
14) I read an abdridged edition of Heart of Darkness by Oxford.

4. written on it or in it?

10. is...will but was...would (sequence of tense.
13. I explained to them

Sra