Which statement about the results of the crusades is not true?
a. europeans learned about science and medicine from the islamic world.
b. tensions between jews and christians increased because crusader armies had slaughtered jews.
c. the holy land remained firmly under the control of christian crusaders.
d. muslims and christians blamed each other for the series of bitter wars.
a?

It is letter A.  Europeans learned about science and medicine from the Islamic world. The Muslims did control Jerusalem for a time, that they forced the Christians out of it.

In some articles that I have read,  regaining control of the historic lands of Canaan and Judea by the Jews, creating their own state in the ancient territory of Israel, is also not a result of the crusades.

b europeans take corn to africa. corn becomes an important crop there.

the answer is a. the harappan civilisation is also called the indus valley civilisation, this is because they built their cities along the indus river. the reason behind this location can be found in the rest of the "old world" civilisations like mesopotamia or egypt, the first built their cities along the rivers tigris and euphrates, the second along the nil; : their respective civilisations thrived because the overflowing of their respective rivers produced favorable conditions for agriculture, their main support.