1.An ordinary car doesn’t run as/so fast as a sports car

→A sports car runs faster than an ordinary car.

$S_{1}$ + not + V + as/so + adv + as + $S_{2}$.

→$S_{2}$ + V + adv + er/more + adv + than + $S_{1}$.

2. Although there are cultural exchanges between ethnic groups, they still keeps the identity of their own culture

→Inspite of having cultural exchanges between ethnic groups, they still keeps the idenity of their own culture.  

Although S + V, S + V.

→In spite of + cụm DT/V_ing, S + V.

3. Nga has just helped him with the housework .

→He has been just helped with the housework by Nga.

S + V + O(tân ngữ).

→S(tân ngữ) + be + PII.

4. He was interested in flying kites when he was young.

→He liked flying kites when he was young.

S + be + interested in + V_ing.

→S + like/love/enjoy/... + V_ing.