do you think of the lecture–____but interesting, but I’ve managed to survive it

15．I didn’t see your sister at the meetingIf she _______, she would have met my brother

_______ is this pair of glasses — I think they are our_______.

The invention of spaceships makes ________ human beings to travel to the moon

ong you have done to him is terrible,for _____ you should make an apology to him, I think．