: Magnification power of a compound microscope is calculated by (a) magnifying power of eye piece * magnifying power of mirror (b) magnifying power of eye piece * magnifying power of objective (c) magnifying power of objective magnifying power of plane mirror​

Answer:

A firewall is software or firmware that prevents unauthorized access to a network.

Answer:

Your first sentence uses the simple past (Did you buy ...?) and your second sentence uses the present perfect (Have you bought ...?). Sometimes there is a difference in meaning between these two forms, but in your example there is not.  

In the sentence pairs below, there is a difference in meaning. The sentences in the simple past describe something that is over, while the sentences in the present perfect, have/had + the past participle, describe an action or situation that still continues in the present.  

Simple past:      I ate a lot of cake. (I’m finished eating cake.)

Present perfect: I’ve eaten a lot of cake. (I may eat more cake.)

Simple past:      I lived in London for three years. (I don’t live in London anymore.)

Present perfect: I have lived in London for three years. (I still live in London.)

Simple past:      Why didn’t you send me any messages? (The time for sending messages is over.)

Present perfect: Why haven’t you sent me any messages? (You can still send me a message.)

Explanation:

Answer:

rooms in my house were arranged in a random pattern

Answer:

The rooms were not regularly arranged. ... Some rooms had to be reached by short flights of stairs. The big sitting room faced the landing steps.

Explanation:

you have to search on internet

Answer:

Al2 (SO4) 3.24H2O है। यह फिटकिरी को पोटेशियम सल्फेट और एल्यूमीनियम सल्फेट की समतुल्य मात्रा से युक्त घोल से क्रिस्टलीकृत करके तैयार किया जाता है। यह एक रंगहीन, क्रिस्टलीय ठोस है जिसमें खट्टा स्वाद होता है। पोटाश फिटकरी का क्रिस्टल आकार में अष्टधातु का होता है।