1.

a. inasmuch as

b. so

c. since

d. hence

2.

a. Taxis are used by a lot of people as they are a good place to deliver a message.

b. There is such a variety of street food that's why it's difficult to choose.

c. The flower market tooks us the whole morning to go around because it was really big.

d. Since there are so many different sounds in the city, it can be confusing.