1.

If Marie Antoinette   (NOT MARRY) Louis XVI,
she   (NOT LOSE) her head.

2.

Shakespeare   (NOT WRITE) plays if
he   (NOT BE) an actor.

3.

If Pierre and Marie Curie   (NOT DO) research into radioactivity, they   (NOT WIN) the Nobel prize in 1903.

4.

If sixteenth century explorers   (NOT BRING) tobacco from the Americas to Europe, fewer people   (SMOKE) today.

5.

Russia   (NEVER BECOME) an important European power, if Peter the Great   (NOT MODERNISE) the country at the beginning of the eighteenth century.

6.

People   (KNOW) less about our modern world
if television   (NOT INVENT).